A study of the low-energy level structure of 165Dy

Nuclear Physics A514 (1990) 173-224 North-Holland

A STUDY

OF

THE

LOW-ENERGY

LEVEL

STRUCTURE

OF

t6SDy

E. KAERTS ~ and P.H.M. VAN ASSCHE

IKS, Leuven University, B-3030 Leuven, Belgium and SCK/CEN, B-2400 Mol, Belgium S.A. K E R R 2, F. H O Y L E R 3 and H.G. Bt~RNER

lnstitut Laue-Langevin, 1=-38042 Grenoble, France R.F. CASTEN and D.D. W A R N E R 4

Brookhaven National Laboratory, Upton, New York, 11973, USA Received 28 September 1989 (Revised 23 November 1989)

Abstract: Thermal

and average resonance neutron capture studies on targets of enriched ~64Dy203 have been performed. The secondary gamma-ray spectra after thermal neutron capture were studied with bent-crystal diffraction spectrometers while the primary gamma-rays were measured with pair spectrometers. As a result, a detailed level scheme for 16SOycomprising 50 levels below 1.5 MeV has been established. The level scheme construction was based on the Ritz combination principle using the very precise secondary gamma-ray energies. The neutron separation energy was found to be 5715.76 (30) keV. Up to about 1.4 MeV, the level scheme is believed to be essentially complete in I =½ a n d ~ levels of both parities. In this energy range, the levels have been grouped into 14 rotational bands. The intrinsic structure of these bands is interpreted on the basis of the present (n, y) results in combination with previously published (d, p) data. It is shown that as a consequence of the quasiparticle-phonon interaction most low-lying levels have a strongly mixed intrinsic structure wih both a one-quasiparticle and a collective vibrational character. Between 500 keV and 1300 keV, as much as six rotational bands with a predominantly vibrational structure have been observed. N U C L E A R R E A C T I O N S 164Dy(n, y), E' = thermal, 2 keV, 24 keV; measured Ev, 1v. t65Dy deduced levels, J, rr, y-branchin.g, band structure, neutron binding energy. Curved crystal spectrometers, HPGe pair spectrometers, enriched targets.

1. Introduction The intrinsic structure

of the low-lying

both in terms of one-quasiparticle

levels in odd-A

excitations

nuclei must be interpreted

and in terms of collective vibrational

Present addresses: z Centre de Recherche du Cyclotron-UCL, Chemin du Cyclotron 2, 1348 Louvain-la-Neuve, Belgium. 2 BP, Nuclear Geophysics Section Research Centre, Sunbury on Thames, UK. 3 Physikalisches Institut A u f der Morgenstelle, D-7400 Tiibingen, Fed. Rep. Germany. 4 Daresbury Laboratory, Warrington, WA4 4AD, UK. 0375-9474/90/$03.50 © Elsevier Science Publishers B.V. (North-Holland) July 1990

174

E. Kaerts et al. / t65Dy

excitations. These latter originate from the coupling of the unpaired nucleon with the vibrational modes of the even-even core. In deformed nuclei, both parallel and anti-parallel couplings of each even-even vibrational mode (if K # 0) with each quasiparticle state occur. One expects therefore that the vibrational spectrum in these odd-A nuclei is m a n y times richer than in the even-even neighbours. Because of the quasiparticle-phonon interaction, however, most rotational bands in deformed odd-A nuclei have a mixed intrinsic structure with both a quasiparticle character and a vibrational character. This situation of course hampers the location of the odd-A vibrational states and explains why in most odd-A nuclei only a few of these albeit numerously present - states have been recognised. Especially for those odd-A nuclei of which the even-even core possesses some low-energetic vibrational modes, the influence of the quasiparticle-phonon coupling on the intrinsic structure can already be observed at low excitation energies. In this respect, 16SOy is a good choice to study the quasiparticle-phonon interaction since the even-even core - 164Dy - possesses two vibrational excitations with K # 0 below 1 MeV; namely a K ~ = 2 + g a m m a vibration at 762 keV and a K ~ = 2- octupole vibration at 977 keV [ref. 1)]. A successful study of the intrinsic structure of low-lying states in deformed odd-A nuclei can benefit from the combination of (n, y) results with results from (d, p) and (d, t) transfer reactions. The (n, y) reaction on one hand, is not structure selective and is therefore perfectly suited to build detailed decay schemes for a large number of low-lying levels. Although these decay schemes can often disclose the major c o m p o n e n t in the intrinsic wave function, it is in most cases not possible to get a detailed picture of the intrinsic structure simply and solely on the basis of these non-selective (n, y) results. (d, p) and (d, t) reactions, on the other hand, are structure selective and populate only states through their one-quasiparticle amplitudes. Moreover, these one-quasiparticle components can be identified by means of the so called "fingerprint method". In combination with the (n, y) results, (d, p) and (d, t) work therefore allows to obtain a more complete picture of the low-energy intrinsic structure in odd-A deformed nuclei. The extended level scheme of ~65Dy which will be presented in this communication results from the following experiments: the measurement of the primary and the secondary gamma-transitions after thermal neutron capture at the high flux reactor ( H F R ) of the Institut Laue-Langevin (ILL) in Grenoble; the measurement of the secondary gamma-transitions after thermal neutron capture at the BR2 reactor of the Studiecentrum voor Kernenergie ( S C K / C E N ) in Mol and the measurement of the primary g a m m a transitions after average resonance neutron capture (ARC) at the high flux beam reactor (HFBR) of the Brookhaven National Laboratory (BNL) in New York. As a result of this (n, 7) work, a detailed and at the same time reliable level scheme for 165Dy has been established. A preliminary report of these results appeared in ref. 2). Prior to this work, the levels of 165Dy had been studied using (n, 7) spectroscopy 3 5); (d, p) spectroscopy 6,7), (n, e - ) spectroscopy 8.9) and 7-spectros-

E. Kaerts et al. / 165Dy

175

copy of radioactive decay ~o). A summary of the results of these experiments is given in the Nuclear Data Sheets compilations of mass 165 [refs. n.~2)]. The (d, p) data from the work of Grotdal et al. 7) will be used in the present study to identify the low-lying one-quasiparticle components in 165Dy.

2. Thermal neutron capture measurements

2.1. INTRODUCTION The primary and secondary y-transitions emitted after thermal neutron capture in 164Dy were studied at the H F R of the ILL in Grenoble. The primary y-rays were measured with the pair spectrometer while the secondary T-rays were measured with the bent-crystal diffraction spectrometers GAMS1 and GAMS2/3. The target, which consisted of 20 mg Dy203-powder enriched to 95.7% in 164Dy, was irradiated in a thermal neutron flux of 5.5 x 10 TM cm -2 s -1. Due to the presence of target impurities (161Dy, 162Dy, 163Dy) the occurrence of multiple neutron capture and the fl- decay of some reaction products (165Dy, 166Dy, 166Ho), the experimental y-spectrum contained contributions from several isotopes. 2.2. PRIMARY y-RAYS FOLLOWING THERMAL NEUTRON CAPTURE The high-energy y-rays (E~ > 3.5 MeV) emitted after thermal neutron capture in the Dy203 source were measured with a pair spectrometer. The special geometry of this spectrometer, which consists of a HPGe detector placed between two NaI(T1) crystals, permits the detection of the creation of an electron-positron pair in the Ge detector. Owing to this, the double-escape processes can be selected while the photo- and the single-escape processes are suppressed. The resolution of the pair spectrometer lies between 2.3 keV, for E~ = 2.3 MeV, and 5.5 keV for E~ --- 7.6 MeV. A detailed description of this spectrometer has been given by Warner et al. 13). The pair spectrum contained 333 y-lines between 3524 keV and 7739 keY. A large number of these transitions belong to 162Dy [ref. 14)], 163Dy [ref. 15)], 164Dy [ref. 16)], 166Ho [ref. 17)] and 28A1 [ref. 18)]. 28A1 was produced by neutron capture in the aluminium foil which surrounded the source material. A partial differentiation between 165Dy and 166Dy lines in the pair spectrum was possible because of the difference in the neutron binding energies ( - 1.3 MeV) for the two isotopes ~9). The energy calibration of the spectrum was performed via transitions from the reaction 27Al(n, T)2SAI [ref. 18)]. The intensity calibration was based on the absolute intensities of a few strong primary transitions in 165Dy [ref. 11)]. Finally, all transitions whose energies differ from the neutron binding energy in 165Dy (Bn = 5715.76 keV) by less than about 2 MeV and whose intensities are larger than 20 photons/ 105 neutron captures in 16aDy [ref. 5)] were assumed to be primary 165Dytransitions. They are listed in table 1.

E. Kaerts et al. / J65Dy

176

TABLE 1 Primary 164Dy(nth, y)165Dy transitions

b)

B -E v ) (keV)

E~(AE~) ) (keV)

l b)

Iv

B, - E v c) (keV)

5143 4204 894 1234 1099 906 27 43 163 789 225 35 141 88 208 119 47 150 116 27 124 21 33 255 22 1477 80 358 85 295

108.25 (6) 158.65 (6) 538.61 (5) 570.19 (5) 573.54(5) 605.06 (5) 911.90 (5) 1015.98 (5) 1079.94 (4) 1103.03 (5) 1108.11 (5) 1158.13 (5) 1166.80 (4) 1218.24 (7) 1256.44 (5) 1376.25 (5) 1380.91 (9) 1400.30 (5) 1440.46 (5) 1444.81 (9) 1464.87 (6) 1501.30(12) 1555.20 (8) 1560.14 (6) 1587.62 (21) 1591.90 (6) 1623.29 (7) 1631.96 (6) 1634.64 (10) 1648.32 (29)

4044.580 (72) 4021.834 (135) 3985.286 (125) 3960.839 (91) 3944.956 (70) 3919.879 (76) 3901.247 (86) 3885.278 (75) 3881.183 (84) 3843.055 (86) 3839.934 (80) 3830.015 (112) 3825.091 (112) 3819.846 (83) 3800.270 (106) 3771.906 (92) 3752.906 (114) 3746.739 (111) 3727.524 (112) 3708.190 (96) 3673.901 (120) 3652.248 (220) 3649.917 (124) 3627.641 (113) 3608.652 (109) 3603.083 (122) 3555.337 (131) 3537.181 (113) 3528.643 (114) 3524.844(120)

50 33 20 437 256 71 109 512 73 105 406 42 47 310 27 335 215 321 31 366 31 21 90 255 373 61 333 354 457 143

1671.18 (7) 1693.93 (14) 1730.48 (13) 1754.92 (9) 1770.81 (7) 1795.88 (8) 1814.51 (9) 1830.48 (8) 1834.58 (9) 1872.71 (9) 1875.83 (8) 1885.75 (11) 1890.67 (11) 1895.92 (8) 1915.49 (11) 1943.86 (9) 1962.86 (12) 1969.02 (11) 1988.24 (11) 2007.57 (10) 2041.86 (12) 2063.51 (22) 2065.84 (12) 2088.12 (11) 2107.11 (11) 2112.68 (12) 2160.42 (13) 2178.58 (11) 2187.12 (11) 2190.92 (12)

Ev(AE~) ~) (keV) 5607.508 (55) 5557.109 (60) 5177.152 (50) 5145.574(44) 5142.223 (45) 5110.699 (47) 4803.859 (50) 4699.785 (48) 4635.820 (35) 4612.730 (45) 4607.648 (44) 4557.629 (51) 4548.961 (37) 4497.520 (63) 4459.320 (50) 4339.508 (46) 4334.848 (88) 4315.465 (45) 4275.305 (50) 4270.949 (87) 4250.887 (52) 4214.461 (114) 4160.559 (79) 4155.617 (60) 4128.144(208) 4123.859 (55) 4092.467 (68) 4083.805 (63) 4081.119 (98) 4067.441 (290)

c

a

a) An additional systematic error of 0.2 keV should be assumed. b) Photons per 105 neutron captures in ~64Dy, percentage errors amount 15%. c) Bn(165Dy)= 5715.76 keV (see subsect. 4.1).

2.3. SECONDARY 3,-RAYS FOLLOWING THERMAL NEUTRON CAPTURE 2.3.1. S e c o n d a r y

y-ray measurements

at the H F R

in Grenoble.

The secondary

y - r a y s e m i t t e d a f t e r t h e r m a l n e u t r o n c a p t u r e in t h e D y 2 0 3 s o u r c e w e r e m e a s u r e d with the bent-crystal diffraction spectrometers GAMS1 and GAMS2/3.

A detailed

d e s c r i p t i o n o f t h e s e s p e c t r o m e t e r s is g i v e n b y K o c h et al. 2o). S e c o n d a r y y - r a y e n e r g i e s a n d i n t e n s i t i e s w e r e m e a s u r e d in t h e r e g i o n b e t w e e n 46 k e V a n d 2500 keV. T h e e n e r g y i n t e r v a l b e t w e e n 46 k e V in first o r d e r a n d 750 k e V in fifth o r d e r w a s r e c o r d e d w i t h G A M S 1 t a k i n g a n g u l a r steps o f 0.9". A t t h e s a m e

177

E. Kaerts et al. / 165Dy ORDER 5

104 _ N ~D "-O'~

O~

.

~ .

¢,3t~ °

•

•

tOcO',.4 " "

' °

Z~ Z,

.

°

(.D

¢~t

•

.

.

.

O O tt~

"~cO

tO

O

0

O

o~ o, o , o , o , o , o ~

10:

lO: 17500

I

|

I

I

I

I

I

37000

I

I

I

I

i

I

i

i

i

I

i

i

35OOO

35500

;6000

36500

104-

lO:

ORDER 3

lO: 30500

I

I

I

I

I

I

I

30000

I

I

J

I

29500

29000

lO 5 .

N!

ORDER 2

lO 4

\ 10~

27000

~

i

i

i

i

i

i

26500

i

i

' i

26OOO

GAMS 3 INTERFEROMETER POSITION

Fig. 1. Part of the 164Dy(nth, y)165Dy spectrum between 900 and 1020 keV measured in second, third and fifth diffraction order. The complex multiplets from the second-order spectrum are gradually resolved in the higher orders. The listed energies are the final values which are obtained as weighted averages over all the different runs and diffraction orders.

E. Kaerts et aL / ~65Dy

178

time, G A M S 2 / 3 was used to scan the energy region from 104 keV in first order to 2500 keV in fifth order taking angular steps of 0.33". In both cases, the counting time was set at 60 s per point. The spectrum between 112 keV and 2000keV was remeasured in a second G A M S 2 / 3 run. The angular resolution during the GAMS1 measurement varied between 4" and 5" while in the G A M S 2 / 3 measurements values between 0.9" and 1.6" were obtained. In third diffraction order for instance, this corresponds to an energy resolution of 120 eV (360 eV) for a 200 keV (800 keV) line measured with GAMS1 (GAMS2/3). Such a resolution often leads to an energy precision as low as a few eV, as can be seen in table 2. In fig. 1 the same portions of the second, third and fifth order diffraction spectrum measured with the GAMS3 spectrometer are shown. The energy resolution in the different diffraction orders can be written as: AE = 1.7 x n t × 10-6 X Ev2 (E, in keV). Owing to the n -1 dependence, the complex multiplets which appear in the secondorder spectrum are gradually resolved in the higher orders. The diffraction efficiency, on the other hand, decreases with increasing diffraction order. Fig. 2 shows the time dependence of the different nuclear reactions that are observed during the irradiation of the Dy203 source in Grenoble. y-transitions originating from the reactions 164Dy(n,y)165Dy,/3-decay and t65Dy(n, y) show the same time dependence and are characterised by a strong decrease of their intensities

~-~I03

~ss

ylsgHo (n,'-/) / ~-t64HO ~-decay r /_ Oy (n,,y)

~6 10 2

E >

~

"C--/.%y,_.o.~ ~ 163Dy(n,-y)

101

11" Dy(n,~)

'~

161DYj3-decay

/

10"1

/ ~(~ W " '0"2-3 10

J

~\165Dy (n'~/)

J

/ /

Er (n ~) ~ I I 10 20 30 IRRADIATION TIME (DAYS)

I /40

Fig. 2. Time dependence of the different nuclear reactions which occur during the irradiation of an enriched Dy203-target (95.7% t64Dy) in a thermal neutron flux of 5.5 x 1014 cm -2 s -I. The reactions 16aDy( n, T), 165Dy(n, 31) and the '65Dy fl-decay show the same time dependence.

E. Kaerts et al. / t65Dy

179

with increasing irradiation time. Therefore, ~,-lines belonging to 165Dy, 165Ho and 166Dy could be selected by studying the time dependence of the experimental transition intensities. The 165Ho lines from this set could be identified by comparison with the results of a previous 16SOy fl-decay study 21). In order to differentiate between 165Dy and 166Dy lines, it was necessary to remeasure the secondary (n, ~) spectrum in a considerable lower neutron flux. Indeed, 165Dy and 166Dy isotopes are produced by single and double neutron capture in 164Dy, respectively. The ratio of the double to single capture activity in 164Dy can be written as: ~165(t)

4~o.,65[1--exp {--[~(O.165--O.16a)"~A165]t}]

/~164(t) -

,/, (o.,65 - o.164) + a165

(1)

The symbols fl164, fl165: ~: t~164, Crl65:

have the following meaning: the neutron capture activity of 164Dy and 165Dy; the thermal neutron flux; 5.5 x 10 TMcm -2 S-l; the cross section for thermal neutrons of 164Dy and 165Dy; 2700 b and 3900 b; A165: the decay constant of ~65Dy; 8.9 x 10 -5 s -~. Because A165~ ~b(o.165- o'164) and for times t > 0.5 d, eq. (1) can be approximated by: ~165(t)/[~164(t) ~

(D(O.165///~165).

(2)

After half a day irradiation in a flux of 5.5x 1014 cm -2 S -1, 164Dy(n, y) and 165Dy(n, y) lines show the same time dependence (see also fig. 2). Consequently, these lines cannot be differentiated by studying their time-dependent intensity behaviour. Relation (2), however, shows that in this case the ratio fl~65(t)/fl164(t) is just proportional to the neutron flux. Therefore, an unambiguous assignment of -y-lines to both isotopes is possible by measuring the secondary ~/-spectrum emitted during irradiation of the Dy203 source in substantially different neutron fluxes. In this context, the (n, 3/) reaction on J64Dy was remeasured at the bent-crystal diffraction spectrometer installed at the BR2 reactor in Mol. 2.3.2. Secondary v-ray measurements at the B R 2 reactor in Mol. The bent-crystal diffraction spectrometer at the BR2 reactor is designed to study secondary 3,transitions following thermal neutron capture. Instead of the traditionally used quartz crystals, a highly perfect silicium crystal is chosen as analysing crystal. Diffraction occurs from the (2n, 2n, 0) planes. Owing to the relative low thermal neutron flux at the target position (~ ~ 1013 cm -2 s -1) and the excellent reflectivity behaviour of the bent Si crystal (a constant reflectivity up to 1.5 MeV in first and 680 keV in second diffraction order and only a E -1 dependence above these energies, see ref. 22)) the bent-crystal diffraction spectrometer at the BR2 reactor offers an excellent complement to the high flux facilities in Grenoble. A detailed description of this installation has been given by Kaerts et al. 23). The energy interval between 230 keV and 1600 keV was measured in steps of 0.5" with a counting time of 1000 s per step. The experimental line width was 1.7", resulting

80.553 (2)

83.398 (2) 85.644 (2) 86.566 (2) 86.733 ( l l ) R6 0~0 (6)

28

29 30 31 32 aq

(6) (1) (5) (1) (1) (5) (8) (6) (6) (6) (3) (7) (3) (7) (9) (6) (6) (6) (12) (5) (6) (4) (6) (1) (1) (1) (4)

46.456 50.434 52.452 52.889 52.906 54.437 55.108 56.067 56.273 56.588 57.864 60.365 61.393 61.848 63.981 64.312 64.458 64.513 64.757 64.968 66.099 67.695 68.288 72.768 76.587 77.514 79.866

(keV)

E~,(AE./)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

Nr

15 (7) 3864 (1659) 22 (8) 16 (3) 41 (8) 9 (2) 15 (7) 5 (2) 5 (2) 6 (2) 11 (2) 7 (2) 17 (4) 6 (2) 7 (3) 8 (2) 8 (2) 8 (2) 6 (3) 14 (4) 9 (2) 17 (4) 7 (2) 327 (66) 113 (25) 202 (58) 11 (2) 115 (25) 454 (99) 2 (1) 2 (1) 2 (1) 5 (13

iv(Al:,) a)

1175.0

83.4

180.9 76.6 261.8 737.9

976.7 649.0

1320.6

658.0

158.6

Initial state 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 3 2 1 1 2 3 5 2 2

N b)

166Dy

165Ho

165Ho

c)

34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66

Nr

86.954 (2) 89.747 (5) 90.208 (2) 92.366 (6) 92.380 (16) 92.633 (7) 94.178 (1) 94.695 (2) 98.863 (2) 100.630 (15) 100.792(2) 101.175 (1) 102.214 (10) 102.701 (2) 103.147 (13) 104.104 (2) 104.148 (3) 108.157 (3) 109.369 (19) 110.328 (7) 110.362 (9) 110.936 (9) 111.210(7) 112.234 (2) 113.132 (13) 114.532 (11) 115.092 (2) 116.162 (5) 116.760(1) 117.813 (9) 119.349 (6) 119.470(2) 120.561 (5)

(keV)

E~,(AE~,)

12 (2)

3(1)

524 (124)

30 (8)

9 (3) 9 (2)

5(1)

2(1)

11 (5)

2 (1) 4 (1) 2 (1) 11 (3) 15 (4) 11 (5) 3 (2) 3830 (935) 58 (25) 3 (1) 2 (1) 6 (1) 6(2) 33 (7) 11 (3) 57 (11) 41 (9) 2468 (508) 4 (2) 5 (1)

I~,(Alv) ~)

297.7

649.0

108.2

1016.1

186.1

1482.1

360.6

628.8

Initial state

Low-energetic t65Dy, t66Dy and ~65H0 T-transitions emitted after thermal neutron capture in 164Dy

7 2 3 5 2 7 2 5 2 5 2 2 2 2 2 4 2 2 3 2 3 2 3 3 2

2 2 5 4

I

5

2 3

N b)

* 165Ho *

*

*

165Ho

165Ho

c)

67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103

120.855 (3) 121.525 (24) 121.806 ( l l ) 121.898 (10) 122.967 (38) 124.749 (5) 125.227 (42) 127.193 (21) 127.719 (14) 127.913 (20) 128.930(18) 130.370 (20) 130.889 (5) 131.145 (22) 131.604 (56) 132.767 (5) 134.663 (13) 135.871 (19) 138.085 (28) 139.096 (2) 139.877 (16) 142.313 (31) 142.488 (2) 143.300 (10) 146.814(4) 150.223 (14) 150.577 (15) 150.969 (2) 153.798 (1) 154.730 (11) 155.497 (11) 155.547 (3) 155.800 (21) 156.240 (1) 157.421 (3) 159.492 (4) 160.768 (7)

2 (1) 2 (1) 2 (1) 242(25) 15 (1) 6 (1)

1 (1) 2 (1) 3 (1) 222(22)

5 (1)

337.2

1464.8

297.7

28 (6) 11 (3) 970(208)

2 (1)

737.9

1440.5

1218.4

1464.9

705.9

5 (2) 10(3) 2(1)

1 (1) 2 (1) 7 (2) 16 (6) 22 (5) 19 (7) 2 (1) 2 (1) 1 (1) 3 (1) 18 (9)

t65Ho

104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140

161.204 (13) 161.276 (11) 163.539 (2) 165.950 (10) 166.479 (3) 169.671 (9) 170.222 (4) 172.738 (1) 174.554(6) 174.610(21) 174.759 (52) 174.988 (11) 176.367 (5) 176.941 (1) 178.374 (4) 179.364 (9) 179.771 (14) 180.059 (t3) 180.742 (9) 180.931 (10) 184.252 (2) 185.293 (53) 186.100 (6) 189.406 (10) 190.824(17) 191.583 (9) 194.524 (7) 196.231 (10) 196.838 (4) 198.437 (4) 200.266 (47) 201.912 (35) 203.209 (11) 204.425 (23) 206.019 (8) 206.122 (13) 206.294 (9)

3(1)

4(1)

14(1) 8(1) 8(1) 1(1)

3(1) 3(1) 11 (4) 18 895 (1926) 2(1) 16(1) 8(1) 2(1) 6(3)

d)

186.1

184.3

360.6 253.5 261.8

360.6

4(1) 137(13) 1(1)

2(1) 13(1) 801 (86) 119(12) 8(1)

1189.4 1095.2

19(2) 73 (8)

2 2 6 2 7 7 6 9 2 3 3 2 9 10 9 2 3 3 3 2 11 2 9 3 3 7 7 6 7 7 2 2 3 5 3 3 3 166Dy

165Ho

165Ho 166Dy

t66Dy t66Dy

,....

(keV)

207.406 (5) 208.339 (4) 209.647 (23) 212.391 (19) 212.611 (12) 215.254 (12) 215.931 (6) 220.702 (8) 244.488 (22) 225.320 (5) 225.728 (4) 228.400 (4) 228.922 (21) 230.733 (12) 231.036 (19) 231.620 (7) 234.065 (6) 234.525 (3) 235.796 (12) 238.062 (4) 240.521 (9) 245.466 (15) 245.915 (6) 246.997 (2) 248.472 (1) 249.082 (6) 249.490(11) 250.301 (4) 250.612 (34) 251.717 (8) 252.124 (3) 252.509 (3) 253.556 (15)

141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173

Ev(AE./)

Nr

14 (7) 14 (1) 122 (12) 34 (4) 4 (4)

7 (1) 2 (1)

1 (1) 22 (4) 7 (1) 6 (1) 3 (1) 9 (1) 2 (1) 5 (1) 9 (4) 2 (1) 10(1) 7 (1) 5 (1) 23 (2) 25 (2) 100 (10) 1 (1) 1 (1) 4 (1) 46 (4)

13 (1) 18 (2) 7 (1)

L,(AI~,) ~)

1337.1

607.5

533.5 1095.2

1337.1

d)

1400.3

1320.6

1464.8

Initial state 7 11 2 4 3 2 11 2 2 11 8 8 3 3 2 12 12 2 12 12 5 4 5 5 4 5 2 3 2 12 12 13 7

N b)

166Dy

*

*

166Dy

165Ho *

c)

174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206

Nr

TABLE 2--continued

254.778 (8) 255.567 (37) 257.052 (22) 258.217 (6) 259.533 (2) 260.652 (2) 261.771 (2) 262.845 (17) 262.987 (44) 270.215 (2) 270.461 (4) 271.721 (1) 273.439 (2) 275.646(10) 277.238 (11) 277.743 (42) 277.843 (5) 279.761 (2) 281.408 (2) 282.513 (39) 283.019 (8) 283.979 (16) 285.067 (5) 285.799 (12) 286.312(2) 287.197 (29) 287.504 (7) 291.230 (11) 292.893 (10) 294.794 (8) 295.180(11) 296.293 (3) 297.370 (3)

(keV)

Ez,(AE~,)

100 (10) 8 (2) 3 (1) 3 (1) 3 (1) 10 (1) 1 (1) 11 (1) 52 (5)

41 (4) 12 (1) 424(43) 208 (20) 3 (1) 10 (1) 7 (2) 5 (1) 725 (72) 52 (5) 2 (1) 3 (1) 5 (1) 8 (1)

2 (1) 2 (1) 7 (1) 3 (1) 18 (2) 109 (10) 155 (15) 1 (1)

Iv(ALe) a)

1376.3 658.0

1380.9

584.0

360.6 1380.9 1444.7

607.6 533.5 527.0

1189.4 261.8

1337.1 1416.3

Initial state 7 2 14 8 12 18 17 2 2 9 8 14 13 3 11 2 2 14 14 3 2 6 7 6 14 2 4 2 5 7 3 9 14

N b)

165H0

t66Dy

165Ho 166Dy

c)

207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243

300.455 (14) 302.359 (39) 303.890 (66) 304.186 (4) 304.367 (4) 306.068 (7) 306.733 (11) 309.378 (48) 309.941 (2) 311.812 (3) 313.293 (2) 313.655 (8) 316.442 (24) 320.236 (3) 320.549 (5) 322.224 (2) 323.994 (11) 328.328 (2) 329.041 (16) 331.151 (8) 331.817 (25) 332.574 (17) 334.064 (4) 336.299 (4) 338.500 (9) 338.930 (11) 339.225 (10) 342.269 (10) 343.323 (3) 345.849(3) 347.395 (7) 348.529 (48) 349.241 (2) 351.283 (5) 352.574 (2) 354.381(1) 356.659 (5) 1416.3

702.9 605.1 607.6

533.5 649.0 533.5 538.6 1464.8

10(1) 20 (2) 5 (1) 464(46) 105 (10)

15 (4) 1881(189) 29 (3) 200 (20) 428 (43) 54 (6)

1400.3 1456.4 584.0 1464.8 1416.3 1464.8 628.8

1416.3

~)

607.6

1464.8

1444.7

60 (6)

548 (55) 41 (9) 1(1)

5 (1)

12 (1) 19 (2) 9 (4) 25 (2) 30 (3) 36 (3) 5 (1) 7 (1) 15 (1) 25 (2) 36 (3) 1(1) 63 (6)

11 (2) 8 (1)

6 (1) 4(1) 11 (5)

9 2 2 8 2 14 16 2 13 11 10 2 3 7 8 9 2 4 6 11 3 2 7 13 4 3 10 3 14 14 4 2 17 7 16 17 16

244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280

357.063 (7) 357.714 (3) 360.278 (6) 361.349 (9) 361.679 (2) 364.346 (11) 365.724 (7) 366.891(4) 367.094 (4) 368.352 (14) 368.749 (2) 369.218 (13) 372.586 (27) 373.184 (20) 373.521 (16) 374.506(11) 374.903 (2) 376.088 (2) 376.321 (3) 376.832 (4) 377.221 (6) 377.567 (12) 378.487 (4) 378.854 (7) 379.216 (4) 380.045 (1) 381.673 (14) 384.813 (4) 386.011 (2) 387.207 (4) 388.345 (4) 389.334 (4) 391.120 (4) 392.062 (63) 392.663 (2) 393.897 (5) 396.222 (3) 27 27 1390 21 295

(3) (5) (149) (3) (31)

46 (4) 17(1)

11(1) 4396 (448)

61 (7) 12(1) 17 (2) 571 (59) 5(1)

8(1)

9 (2) 24 (3) 15(1) 163 (17) 64 (6) 102(10) 20 (2) 15(1)

5(1)

27 (7) 321 (32) 13 (2) 27 (4) 1265 (558) 10(1) 6(1) 11(1) 23 (2) 15(1) 177 (20)

658.0

573.6

1479.1

1464.8 570.3 649.0

538.6

912.0

1464.8 737.9

533.5 1479.1

1016.1 1456.4 705.9

702.9

538.6 1376.3

4

3 8 2 19 11 18

8

5 17 11

4

3 17

4

15 13 14 9 3 2 15

4

5 11

4

5 3 9 3

4

19 3 2 18 3 3 165Ho

....

(keV)

396.835 (7) 397.962 (9) 399.746 (3) 400.682 (4) 403.073 (1) 405.336 (7) 408.229 (3) 408.453 (6) 411.679 (2) 414.162 (59) 414.997 (3) 419.852 (38) 420.395 (50) 420.840 (3) 422.215 (35) 423.366 (6) 424.161 (8) 425.335 (16) 426.696 (9) 429.950 (12) 430.478 (5) 432.083 (6) 433.402 (13) 436.150 (15) 437.090 (6) 440.169 (13) 441.120 (19) 441.376 (37) 442.548 (41) 443.760 (14) 444.139 (8) 444.564 (10) 446.506 (8)

281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313

E~(AE~)

Nr

113 (11) 32 (3) 164 (22) 47 (6) 48 (5) 567 (63) 45 (5) 5(1) 11 (1) 16 (1) 55 (7) 12 (1) 6 (1) 8 (1) 6 (1) 15 (1) 5 (1) 31 (3)

8 (1) 6 (1) 243 (29) 29 (3) 395 (44) 15 (2) 289 (30) 36 (4) 4931 (531) 17 (6) 4358 (487) 14 (3) 25 (19) 1277 (142)

iv(Air ) a)

705.9 628.8 605.1

1016.1

1175.0 737.9 702.9

538.6 1016.1

607.6 605.1 533.5 607.6

1158.1 605.1

573.6

705.9 1016.1 570.3

1135.8 584.0 737.9 584.0

Initial state 4 3 16 6 18 4 17 3 17 2 17 2 2 16 2 16 8 16 11 12 17 7 3 4 4 12 4 (1) 3 2 5 4 5

N b)

165Ho

¢)

314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346

Nr

TABLE 2-----continued

446.994 (11) 447.915 (2) 449.027 (9) 450.213 (12) 450.984 (13) 451.205 (3) 452.208 (4) 454.404(20) 456.062(7) 459.168 (5) 460.135 (7) 462.103 (3) 462.883 (7) 464.610 (63) 465.427 (3) 469.045 (4) 470.251 (4) 472.023 (13) 473.737 (3) 474.212 (4) 474.945 (3) 477.072 (3) 479.372 (4) 479.613 (6) 480.491 (5) 481.154(12) 482.591 (6) 486.841 (6) 489.908(31) 490.208 (13) 493.471 (15) 495.429 (12) 496.942 (3)

(keV)

Ev( AE ~ )

11 (4) 45 (6) 16 (3) 224 (25) 84 (9) 20 (5) 5153 (576) 157 (16) 1262 (169) 11 (1) 219 (22) 194 (22) 383 (44) 2044(303) 202 (21) 56 (7) 192 (23) 17 (2) 49 (5) 88 (10) 5 (1) 8 (2) 3 (1) 6 (1) 6029 (735)

19 (2) 2454 (250) 10 (1) 11 (1) 27 (3) 76 (8) 57 (6)

I~(AI~) a)

1103.0 605.1

1016.1 1135.8

1218.3

658.0 1103.0 1080.0 658.0 1108.2

570.3 649.0 649.0 573.6 1175.0 628.8

1088.0

1080.0 1158.1

628.8 607.6 1108.2

Initial state 5 7 4 3 3 4 10 2 8 10 5 18 14 3 17 14 15 2 14 12 15 15 14 3 14 3 8 9 1 2 2 2 16

N b)

165Ho

165H0

165H0

c)

e,

347 348 349 350 351 352 353 354 355 356 357 358 359 36O 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383

499.407 500.603 502.111 504.013 506.459 506.980 508.899 509.139 509.772 510.392 510.942 511.465 512.002 512.448 514.426 515.476 517.771 519.054 520.679 524.202 524.983 528.855 529.282 529.451 532.748 533.494 534.617 535.767 537.988 538.634 539.627 541.402 543.925 544.484 545.426 545.837 546.123

(4) (7) (11) (6) (4) (15) (3) (7) (6) (29) (28) (29) (45) (5) (5) (5) (11) (4) (6) (2) (4) (12) (4) (14) (23) (9) (4) (3) (34) (3) (15) (5) (32) (87) (33) (6) (6)

10(3) 217(25) 67 (7)

227 (23) 58(6)

2o (3)

736 (73) 114 (18) 9331 (951)

445 (44)

455 (46) 176(18) 26 (3) 76 (8) 241 (25) 10(2) 344 (34)

25 (2)

125 (27) 47 (6) 41 (4) 36 (4) 37 (4) 31 (5) 43 (4) 192 (24) 1286 (129) 10(1) 131 (13)

852 (88)

1915 (214) 1453 (146) 10(1) 201 (20) 828 (83) 31(5)

1175.0

1080.0

538.6

d)

1158.1 1103.0 1103.0 533.5 1108.2 1140.9

1088.0 1103.0 628.8 1108.2 705.9

1140.9 1218.3 1088.0

1088.0 1080.0 1135.8 1166.9 1158.1 1080.0

658.0 584.0

4 6 8 3 6 4 8 8 6 2 8 2 8 8 5 2 7 3 7 3 2 2 6 4

1 1 1

16 7 3 7 8 2 8 5 4 1

165Ho

165Ho

384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 588.966 (42) 589.490 (13)

588.535 (17)

546.543 (2) 547.197 (23) 548.725 (54) 549.371 (3) 549.811 (27) 550.513 (16) 550.643 (25) 551.814 (5) 552.552 (17) 553.002 (10) 553.570 (58) 554.521 (11) 556.938 (6) 558.563 (31) 559.000 (43) 560.352(7) 561.794(4) 562.227 (5) 563.038 (55) 564.409 (2) 565.578 (3) 565.718 (9) 567.318 (13) 568.113 (74) 569.566 (6) 570.604(6) 574.122 (3) 574.705 (6) 575.561 (4) 579.141 (33) 579.979 (30) 583.994 (4) 584.524 (17) 586.907 (13) 1135.8 1158.1

36 (3)

1218.3

584.0 1158.1

1140.9 1158.1 1108.2

d)

1175.0

1103.0 649.0

1218.3 1166.9 1135.8

1088.0 737.9

1088.0 658.0

253 (29) 10(1) 17 (2) 31 (4) 55 (5)

20 (3) 310(31) 8.(1) 5 (2) 19 (1) 53 (5) 39 (5) 5 (1) 468(47) 495 (50) 155(17) 39 (7) 18 (5) 824 (84) 600(60) 156(15) 43 (4) 101 (10) 13 (2) ll (1) 3100(316) 79 (11) 11 (1) 12 (1) 7 (2) 22 (2)

1080.0

392(39)

11 5 4 4 2 9 9 10 8 8 3 3 11 5 4 4 2 3

1

3 2 6 2 5 3 5 10 2 2 5 7 6

1

8 2 2 11

165Ho

165Ho

t65Ho

Y.

t.-,

(keV)

590.963 (14) 592.015 (37) 593.283 (12) 594.859 (78) 595.700 (17) 596.626 (3) 597.167 (8) 598.560 (33) 600.470 (23) 601.366 (6) 602.244(8) 603.478 (39) 605.016 (33) 607.176 (11) 607.960(15) 610.453 (36) 610.793 (35) 612.130 (24) 612.499 (34) 613.259 (3) 614.302 (26) 617.042 (28) 619.480 (10) 620.642 (18) 621.812 (17) 622.408 (6) 624.235 (23) 626.923 (33) 627.566 (11) 630.005 (60) 631.438 (21) 633.428 (12) 636.279 (14)

421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453

ET(AEv)

Nr

130 (26) 43 (11) 6 (1) 58 (11) 19 (6) 6 (1) 817 (165) 56 (18)

9 (2) 10 (2) 16 (3) 15 (3) 367 (73) 11 (2) 8 (1) 185 (37) 181 (36)

65 (6) 10 (1) 28 (3) 6 (1) 23 (3) 623 (65) 127 (13) 6 (1) 10 (1) 44(9) 37 (7) 21 (4) 6 (1) 48 (9)

l:,(dlv) a)

1158.1

1218.4

1218.4

1175.0 1140.9

1166.9 1135.8 1256.5

1166.9

1175.0

Initial state

5 4 2 6 3 1 1 3 2 9 2 2 8 7 4 7 2 2 8 2 2 9 5

N b)

165Ho

t65Ho *

* 165Ho

c)

454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486

Nr

TABLE 2 - - c o n t i n u e d

636.410 (42) 639.624(24) 641.441 (15) 642.032 (45) 642.576 (15) 644.768 (11) 646.721 (19) 647.552 (55) 648.307 (13) 648.962 (5) 650.555 (9) 651.434 (32) 651.733 (12) 654.105 (51) 656.248 (11) 658.400 (41) 659.776(46) 660.137 (31) 662.455 (11) 663.241 (83) 665.287 (22) 666.702 (30) 671.632 (20) 672.336 (20) 672.904 (194) 674.867 (94) 675.218 (9) 676.331 (29) 678.283 (18) 680.116 (32) 682.384 (96) 683.767 (36) 684.936 (25)

E~,( AE v) (keV)

8 (1) 22 (4)

11 (2) 8(1) 20 (4) 22 (4) 18 (5) 20 (4) 71 (14) 10 (2) 17 (3) 8 (1)

32(6) 40 (8) 72 (14)

43 (8) 10(3) 27 (5) 8 (2) 68 (14) 31 (6) 27 (5) 8 (2) 31 (6) 271 (54) 53 (11) 46 (17) 31 (6) 3 (1) 40 (8)

l~,(Aiv) a)

1256.5 1380.8 928.7

1256.5

649.0

1218.3

1175.0

1175.0

Initial state

3 6 2 3 2 4 2 4

(1)

2 4 5 2 6 5 5 2 3 8 6 3 3 2 5 2 4 5 6 2 2 2 2 3

N b)

166Dy

165Ho 166Dy

c)

t~ ,....

487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523

686.293 (42) 687.684 (26) 690.582 (19) 692.514 (13) 694.057 (31) 698.271 (70) 699.061 (17) 700.079 (20) 700.633 (28) 704.291 (41) 706.131 (31) 706.688 (38) 707.312 (23) 711.288 (6) 714.556(64) 715.336(3) 716.983 (28) 717.804 (36) 718.210 (69) 721.414(66) 725.380 (20) 726.671 (24) 727.267 (28) 728.819 (24) 730.578 (119) 731.553 (56) 731.871 (23) 742.264(15) 742.789 (57) 743.739 (87) 744.037 (14) 745.139 (26) 746.137 (11) 572.507 (18) 753.717 (14) 754.298 (8) 757.397 (29)

34(6) 45 (9) 52 (10) 31 (6) 42 (8) 222 (44) 17 (4)

22 (4) 24(4) 13 (2) 31 (6) 15 (3) 29 (5) 243 (48) 72 (17) 903 (181) 20 (4) 39 (9) 22 (5) 10 (2) 32 (7) 17 (3) 17 (3) 13 (3) 13 (3) 37 (8) 39 (7) 37 (7) 15 (3)

25 (5)

15 (3) 57 (11) 49 (9) 118(23) 16(3) 12 (3)

1016.1

1380.8 1400.3

1256.5 1376.3

1309.3

1256.5

4 6 2 2 4 3 5 5 4 6 3

1

2 5 5 9 4 2 5 2 2 2 2 1 2 11 3 11 3 5 3 2 4 4 2 4 2 165Ho

165Ho

t65Ho

524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560

759.114 759.774 763.027 763.799 766.761 767.949 768.951 769.907 771.052 775.705 776.639 780.571 783.562 786.491 788.290 790.581 791.342 792.385 793.768 795.304 796.946 798.398 800.950 801.973 803.143 805.320 807.344 807.987 809.862 811.248 812.801 815.691 816.272 818.252 819.563 820.146 821.406

(51) (51) (31) (35) (23) (94) (84) (6) (39) (42) (17) (6) (28) (63) (18) (50) (59) (20) (33) (62) (11) (7) (48) (17) (46) (47) (91) (33) (76) (11) (60) (24) (14) (16) (53) (46) (49)

24(5) 165 (35) 17 (4) 55(11) 88(17) 51 (10) 27 (5) 26 (5) 20 (4)

28 (6) 22 (4) 25 (7) 14 (3) 72 (16) 342 (68) 11 (3) 101 (20) 22 (7) 17(3) 25 (5)

11 (4)

15 (3) 11 (2) 14 (3) 16 (3) 22 (4) 31 (7) 48 (10) 189 (39) 25(5) 18 (4) 37 (7) 203 (40) 13 (2) 32 (7) 34 (6)

1400.3

1416.3

1103.0 1380.9

1456.4

1400.3

976.7 1440.5 1376.3

857.2

1380.8

1023.4

3

1 1

2 3 7

1

3 3 2 5

(1)

5 5 6 2 5 9 2 6 2

(1)

3 8 3 2 4

1

2

165Ho

166Dy

t66Dy

r~

e~

(keY)

824.015(27) 826.646 (27) 827.565 (43) 828.569 (17) 831.822 (9) 833.039 (40) 835.093 (48) 835.987 (23) 837.710 (22) 838.162 (25) 839.364(87) 840.519 (39) 841.384 (47) 842.144(57) 842.734 (27) 846.058 (7) 847.436 (86) 848.898 (110) 850.288 (12) 851.382 (52) 852.128 (8) 853.849 (85) 854.948 (94) 856.526 (22) 857.156 (11) 857.607 (37) 858.656 (16) 860.611 (37) 861.224 (82) 861.811 (61) 865.918 (28) 866.590 (21) 867.958 (14)

561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593

Er(AET)

Nr

22 (4) 27 (5) 40 (11) 90 (18) 376 (75) 72 (14) 20 (5) 42 (9) 227 (45) 110 (22) 79 (21) 70 (14) 25 (5) 30 (6) 61 (12) 240 (48) 18 (5) 32 (13) 116 (23) 44(10) 517 (103) 20 (5) 17 (4) 79 (16) 231 (50) 58 (13) 96 (19) 130 (26) 37 (8) 20(5) 29 (6) 46 (10) 61 (13)

IT(AIr ) a)

2 4 5

1444.7 2 2 3 4

1

2 6

1 1

8

1

2 5

1

4 9

(1) (1)

3 5 3 5 9 6 3 4 11 3 2 4

N b)

1440.5 857.2

1103.0 1380.8 1416.3 1416.3 1380.8 1456.4 1479.1 1456.4 928.7

1464.8 1376.3 1135.8

1400.3 1456.4 912.0 1016.1 1482.1

Initial state

166Dy

t66Dy

¢)

594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 62l 622 623 624 625 626

Nr

TABLE 2--continued

871.089 (33) 872.398 (11) 874.229 (22) 876.812(15) 877.775 (30) 880.839 (22) 882.833 (13) 886.092 (29) 887.734 (15) 888.883 (68) 891.319 (25) 893.421 (9) 895.341 (51) 898.434 (34) 900.564 (106) 901.345 (37) 903.736 (19) 905.527 (14) 906.066 (20) 907.096 (18) 911.966 (4) 916.258 (45) 916.947 (13) 918.803 (14) 919.979 (11) 920.666 (11) 921.442 (22) 922.113 (13) 922.785 (31) 923.957 (62) 926.187 (11) 927.222 (31) 928.738 (84)

(keY)

ET(AET) 27 (5) 169 (33) 70 (14) 64(13) 51 (10) 39 (8) 124 (25) 100 (20) 115 (24) 25 (6) 148 (30) 296 (59) 73 (15) 24 (5) 10 (2) 22 (4) 128 (26) 277 (56) 467 (100) 141 (28) 3175 (635) 34 (8) 156 (31) 163 (32) 256 (51) 289 (58) 136 (28) 202 (40) 67 (14) 58 (13) 330 (66) 111 (23) 34 (11)

IT(AIT) a)

1108.2 1464.8 1108.2

1218.3 1080.0 1103.0

1103.0

1088.0 1479.1 1444.7 1088.0 912.0

1464.8 976.8

1464.8 d) 1456.4 1141.3

1444.7 1456.4

Initial state

N b)

t65Ho

166Dy

c)

2 -...

627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663

929.399 (11) 931.351 (10) 932.657 (11) 933.850 (14) 937.361 (44) 943.548 (104) 944.433 (7) 945.815 (121) 946.850(15) 949.622 (21) 950.569 (19) 951.596 (50) 952.430 (76) 953.810 (26) 954.865 (11) 958.658 (46) 961.209 (32) 962.192 (46) 965.316 (12) 967.669 (52) 971.853 (34) 974.027 (69) 976.662 (194) 977.184(47) 979.834(21) 982.257 (24) 985.341 (53) 986.696 (20) 988.146 (89) 989.719 (21) 990.673 (25) 994.012 (26) 994.870 (8) 1003.475(38) 1005.602 (14) 1006.529 (56) 1008.272 (17)

252(52) 161 (32) 291 (59) 1363 (272) 53 ( l l ) 268 (54) 63 (14) 310(62)

32 (8)

97 (19) 41 (8) 236 (47) 55(11) 46 (9) 53 (1 l) 137(35) 490 (102) 995(199) 611(122) 65 (13) 334 (67)

25 (6)

466(93) 488(99) 684(137) 485(98) 67 (13) 37 (11) 823 (164) 37 (8) 122 (24) 88 (17) 89 (19) 52 (11) 25 (6) 77 (16) 425(85)

1166.9

1175.0 1175.0 1103.0

976.8 1135.2 1088.0 1140.9

1080.0

1135.8

1135.8

(1)

1482.1 1103.0 1479.1 1023.4 1108.2

6 8 8 3 7 2 6 6 6 7 3 6 2 5

(1)

2 6 2 4 2 6 2 2 2

1

7 2 4 4 4 2

7 8 7 7 3

1088.0 1464.8 1016.1

t66Dy

664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700

1011.854 (37) 1015.372 (63) 1016.100 (15) 1016.530 (80) 1018.413 (63) 1019.390 (53) 1021.500 (43) 1022.458 (73) 1026.852 (17) 1027.802 (148) 1030.810 (38) 1032.816 (54) 1035.642 (75) 1037.485 (16) 1039.876 (102) 1042.908 (44) 1047.518 (32) 1049.650 (43) 1055.894 (35) 1057.213 (61) 1058.355 (17) 1060.882 (24) 1064.222 (16) 1072.212 (9) 1074.746 (50) 1077.850 (36) 1079.645 (30) 1083.175 (15) 1088.024 (48) 1088.883 (52) 1090.239 (38) 1097.558 (48) 1098.393 (105) 1100.812 (112) 1104.135 (75) 1105.644 (49) 1108.204 (13)

77 (16) 103 (27) 1038 (216) 175 (63) 60 (14) 81 (18) 67 (14) 105 (21) 131 (26) 24(6) 48 (10) 48 (10) 27 (6) 274 (55) 46 (11) 67 (14) 477 (95) 117 (27) 80 (16) 83 (18) 1028 (206) 151 (30) 189 (38) 1680 (336) 111 (22) 126 (26) 171(35) 392 (84) 96 (20) 69 (15) 88 (18) 71 (15) 51 (10) 51 (12) 57 (13) 86 (18) 734 (149) 1108.2

1380.8

1256.5 1158.1

1309.3

1140.9

1135.8

1016.1 1175.0

2 2 7

1 1

3 4 2 2 2 3

1

2 2 2 4 6 2 2 3 2 6 2 3 8 4 3 2 8 5 5 8 3

(1)

3 2 6

165Ho

t~

(keV)

1109.556 (41) 1112.459 (96) 1113.900(59) 1121.565 (130) 1122.834 (69) 1125.032 (20) 1128.402 (102) 1131.253 (30) 1132.470 (27) 1134.381 (39) 1136.433 (38) 1139.769 (81) 1142.732 (80) 1144.605 (48) 1146.065 (91) 1148.128 (68) 1149.271 (166) 1150.547 (83) 1151.612 (81) 1154.906 (73) 1158.083 (31) 1159.154(94) 1160.633 (83) 1161.826 (100) 1162.992 (113) 1166.464 (208) 1170.830 (38) 1178.458 (36) 1181.315 (59) 1182.982 (46) 1184.307 (34) 1185.458 (59) 1186.517 (130)

701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733

E~,(AE~,)

Nr

15 (4) 32 (7) 37 (8) 62 (13) 336 (69) 67 (14) 53 (11) 57 (12) 34 (8) 34 (9) 62 (12) 1020 (205) 148 (33) 180 (38) 211 (44) 110 (24) 50 (14)

399 (82) 60(12) 62(13) 82 (17) 91 (19) 288 (62) 55 (17) 170 (34) 194(39) 58 (12) 60 (12) 27 (6) 43 (9) 58 (12) 29 (6)

iv(A/v ) a)

1337.1 1479.1 1444.7 1482.1

1320.6

1158.1

1309.3

1320.6 1320.6 1440.5

1309.3 1309.3

1482.1

Initial state 5 (2) (2) 3 2 5 (2) 3 3 3 3 2 3 3 2 3 2 3 2 2 4 2 2 2 2 2 3 6 2 2 3 2 2

N b)

¢)

734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766

Nr

TABLE 2--continued

1189.761 1191.320 1192.177 1195.438 1198.899 1199.973 1201.148 1203.187 1206.290 1212.511 1216.250 1217.720 1219.225 1220.317 1221.492 1222.319 1223.745 1225.248 1226.612 1227.985 1228.935 1230.252 1232.010 1240.430 1241.637 1246.770 1256.102 1256.624 1257.683 1259.056 1260.531 1261.575 1263.248

(24) (83) (67) (166) (69) (91) (112) (61) (55) (211) (36) (53) (33) (71) (92) (56) (41) (39) (50) (90) (50) (74) (41) (52) (36) (63) (90) (151) (46) (71) (19) (125) (93)

Ev(AE~) (keV)

1444.7

612 (131) 102 (23)

1416.3

1440.5

1400.3

1337.1

1380.8

1376.3 1400.3 1482.1

1320.6

1380.9 1309.3 1464.8

1376.3 1376.3

Initial state

174(35) 86 (18) 72 (16) 207 (49) 65 (14) 66 (18) 41 (11) 155 (33) 72 (15) 34 (8) 195 (44) 152 (32) 253 (63) 98 (22) 107 (25) 212 (44) 199 (41) 187 (39) 93 (19) 91 (19) 163 (34) 69 (15) 223 (54) 126 (26) 316 (63) 81 (17) 226 (53) 261 (77) 343 (70)

iv(d/v ) a)

3 4 2 4 3 2 2 2 2 (2) 3 2 3 2 2 3 2 2 2 2 3 2 5 2 7 3 2 3 4 3 6 3 2

N b)

~)

767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803

1264.553 (149) 1268.133 (33) 1272.550 (239) 1273.836(63) 1275.421 (119) 1278.268 (69) 1280.628(37) 1282.089 (45) 1283.344(143) 1285.933 (68) 1286.971 (97) 1289.218 (102) 1292.028 (42) 1297.865 (36) 1300.253 (92) 1301.342 (95) 1302.941 (85) 1306.204(82) 1316.790 (43) 1320.446 (39) 1322.161 (71) 1323.437 (84) 1325.781 (276) 1338.973 (127) 1343.132 (72) 1344.241 (171) 1345.578 (52) 1347.009 (112) 1349.216 (51) 1350.395 (141) 1351.845 (63) 1354.686 (137) 1370.916 (32) 1373.530 (172) 1374.546 (133) 1378.255 (59) 1380.237 (28)

275 (56) 58 (16) 131 (27) 143 (29) 358 (72)

1479.1 1482.1

2

2 2 4

(2)

2 3 3

(2)

2

(2)

2

(1)

(2)

3 3 2 2 2

(2)

3 3 2 2 2

(2)

2 2

(2)

4 3

(2)

2 4 3 2 2

58(15)

1482.1

1479.1

1482.1

1400.3 1456.4

1464.8

1456.4

1376.3 1456.4

122 (26) 63 (18) 192(39) 62 (15) 268(55) 89 (20) 105(22)

57 (17) 233 (54) 108 (22) 114(24) 122 (25) 69 (15) 180 (48) 133(27) 34(9) 167(35) 124(27) 53 (13) 715 (144) 296 (61) 83 (18) 96 (21) 112 (26) 86 (20) 193(41) 211 (43) 114(25) 148(31) 133(31)

804 805 8O6 807 808 809 810 811 812 813 814 815 816 817 818 819 82O 821 822 823 824 825 826 827 828 829 83O 831 832 833 834 835 836 837 838 839 84O

1383.952 (105) 1386.201 (284) 1391.691 (23) 1396.615 (53) 1398.550 (36) 1401.401 (26) 1405.508 (150) 1407.675 (108) 1409.172 (183) 1410.907 (22) 1412.162 (124) 1418.866 (56) 1421.023 (57) 1428.141 (248) 1429.598 (201) 1433.247 (25) 1435.046 (121) 1436.932 (112) 1438.410 (192) 1442.184 (218) 1447.091 (100) 1448.681 (81) 1450.496 (146) 1451.828 (188) 1453.695 (175) 1458.759 (75) 1464.196 (103) 1466.973 (244) 1470.646 (79) 1475.859 (86) 1477.698 (99) 1479.898 (166) 1483.676 (35) 1509.380 (121) 1511.866 (195) 1512.746 (106) 1514.349 (214) 135(31) 46 (14) 100 (21) 122 (24) 77(17) 107 (23) 124 (25) 122 (20) 102 (23) 115 (25) 135 (28) 174 (36) 249 (52) 112 (25) 858 (184) 95 (22) 274 (66) 376 (103) 135 (30)

181 (38)

79 (18) 25 (9) 559 (116) 284 (59) 337 (68) 514 (105) 76 (20) 112 (26) 74 (20) 884 (184) 86 (21) 138 (28) 121 (24) lO0 (23) 58 (16) 523 (105) 102 (23)

3 3 2

(2)

2 2 1 2 5

(1) (2) (2) (2) (2) (2) (2) (2) (2)

2 (1) 6 2 3 5 2 2 2 7 2 2 2 2 2 5 2 2 2

7~

.....

1517.108 (138) 1521.321 (103) 1523.590(114) 1526.118 (241) 1528.521 (102) 1531.267 (229) 1533.037 (61) 1534.671 (222) 1539.118 (75) 1540.591 (195) 1542.470 (64) 1543.962 (159) 1551.008 (92) 1553.094 (67) 1554.738 (81) 1559.505 (274) 1560.729 (170) 1562.487 (135) 1568.067 (102) 1570.601 (127) 1573.716 (61) 1580.234 (168) 1585.522 (120) 1589.623 (65) 1591.500 (107)

841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865

166 (39) 126 (29) 154 (34) 72 (25) 500 (101) 95 (23) 363 (74) 166 (37) 197 (41) 114(26) 284 (58) 83 (21) 140 (30) 320 (65) 173 (36) 93 (27) 183 (41) 261 (55) 237 (48) 77 (18) 410 (83) 100 (23) 159 (35) 405 (82) 185 (41)

I~(AI~) ~) Initial state 2 (2) (2) (1) 2 (2) 2 2 2 (2) 2 (2) 2 2 2 2 2 2 2 (2) 2 2 2 3 2

N b)

c)

866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890

Nr

1593.043 1595.656 1598.398 1599.893 1604.517 1610.907 1613.202 1616.663 1628.718 1633.221 1646.417 1671.715 1691.674 1706.231 1717.143 1722.061 1736.613 1738.004 1781.335 1835.392 1855.990 1862.182 1866.177 1879.635 1898.980

(209) (80) (122) (128) (57) (117) (159) (155) (73) (68) (65) (67) (130) (219) (69) (85) (244) (99) (83) (119) (116) (99) (68) (126) (118)

(keV)

Ev(AEv) 138 (33) 393 (83) 181 (41) 143 (34) 452 (92) 218 (46) 204 (48) 282 (63) 289 (59) 323 (66) 460 (94) 592 (138) 381 (83) 292 (62) 753 (152) 745 (151) 391 (87) 500 (107) 518 (109) 496 (124) 441 (96) 344(76) 564 (117) 334 (73) 192 (51)

I:,(AI~,) ~)

Initial state 2 2 2 2 2 2 2 2 2 2 2 3 2 3 2 2 2 2 2 2 1 2 2 2 2

N b)

c)

") Photons per 105 neutron captures i n 164Dy. b) N designates the total number of independent measurements of a given transition. c) y-transitions following double neutron capture in 164Dy (166Dy lines) and/3 decay of 165Dy (t65Ho lines) show the same time dependence as 165Dy transitions, y-transitions which showed a clearly different time behaviour but of which the origin could not be determined are also listed in the table and are marked with an asterisk. d) Transitions with a double placement, see table 6.

(keV)

E,(AE,)

Nr

TABLE 2---continued

e,

03

tz o o

70006000'

E. Kaerts et al. / 165Dy GAMS2

193 852.12 3,2+~ 2,0+

906.06

5000. 4000'

857.14 I I ~

3000

~

2

, ~0,0 2 +"

2000"

1000'

350( O

3000-

z oo

2500i

i

J

i

i

i

27100 27200 27300 27400 27500 27600 GAMS 2 INTERFEROMETER POSITION

Fig. 3. Portions of the second-order gamma-spectra measured at the ILL and at the SCK after thermal neutron capture in an enriched Dy203 target (95.7% t~Dy) using bent-crystal diffraction spectrometers. Except for three lines that are not seen in the Mol-spectrum, there is a good correspondence between both spectra. These missing lines are assigned t o 166Dy.

in an energy resolution AE = 2.6 x 10 -6 E2n -1 ( A E and E in keV). The peak to b a c k g r o u n d ratio was 2-5 times lower than in the G A M S 2 / 3 case while the errors on the p e a k positions were 2 - 6 times larger. Because o f the flux d e p e n d e n c e of the d o u b l e to single n e u t r o n capture activity in ]64Dy, 166Dy lines fell below the sensitivity limit o f the Mol instrument. As an example, fig. 3 shows portions o f the y-spectra m e a s u r e d in s e c o n d diffraction order at the Mol and the G r e n o b l e ( G A M S 2 ) facilities. As one can see, there is almost a one to one c o r r e s p o n d e n c e between both spectra. O n l y the three intense lines at 852.13 keV, 857.14 keV and 887.73 keV have not been observed in the Mol experiment. C o n s e q u e n t l y , they must be assigned to ]66Dy" 2.3.3. Secondary y-ray list. Table 2 lists the c o m b i n e d results o f all the bent-crystal diffraction spectrometer experiments. Transition energies and intensities are derived f r o m the G A M S m e a s u r e m e n t s and are weighted averages over all the different runs

194

E. Kaerts et al. / 165Dy

and diffraction orders. Transitions assigned to 162Dy [ref. 14)], 163Dy [ref. 15)], 164Dy [ref. 16)], 166Ho [ref. t7)], 166Er [ref. 17)] and 167Er [ref. 24)] (160 in total) have been omitted. Column 1 gives the relative transition energies. The relative energy calibration was performed in the usual way by requiring that a y-transition has the same energy in all diffraction orders in which it is observed. The relative energies differ from the absolute ones by a factor 1.00024 (6) which was calculated on the basis of the observed K ~ and K~2 X-rays of Ho and Er and the absolute values in ref. 25). The transition intensities in column 2 are given per 105 neutron captures in 164Dy. This calibration was performed on the basis of the absolute intensities of the 50.434, 72.768, 108.157 and 184.252 keV lines ~1). If absolute intensities are needed an extra calibration error of 7% must be taken into account. Column 3 gives the initial level for all y-transitions which could be placed in the level schemes of 165Dy or 166Dy. Column 4 lists for each transition the total number of independent observations. The last column contains information about the origin of a number of y-transitions which could not be assigned to 165Dy. All 165Ho lines and the 166Dy lines above 230 keV were identified as described in the previous paragraphs. 166Dy lines below 230 keV could be recognized by comparing the GAMS results with the (n, y) list from Schult et al. 3), obtained with the Riso bent-crystal diffraction spectrometer during irradiation of an enriched 164Dy target in a thermal neutron flux of 6× 10 13 cm -2 s -1. Transitions which clearly showed a different time dependence than 165Dy lines but which could not be assigned are marked with an asterisk. Finally, it should be noted that transitions between 104 and 1500 keV, which have only been observed once should be considered as doubtful. 3. Average resonance neutron capture (ARC) measurements 3.1. INTRODUCTION

It is known that the intensities of primary y-transitions from a single resonance or thermal neutron capture show statistical fluctuations which are described by a Porter-Thomas distribution 26). In order to reduce these Porter-Thomas fluctuations, it is necessary to average over a large number (preferably >20-30) of compound resonance states. Under these conditions, the reduced primary intensities ( I y / E 5) fall into narrow bands corresponding to rather definite spin and parity values 27). This means that up to a certain excitation energy and for well defined spin and parity values, complete sets of levels will be observed and that for all these levels reliable spin and parity assignments can be made 28). 3.2. EXPERIMENT AND RESULTS

The ARC measurements on 165Dy have been performed at the filtered neutron beam facility at the BNL HFBR. A detailed description of the ARC facility in Brookhaven has been given by Greenwood et al. 29).

5147.8 (1) 5144.0 (7) 5133.7 (3)

5112.4 (1) 5087.7 (9) 4807.5 (4)

4637.9 (1)

4630.0 (1)

4614.8 4610.4 4576.9 4559.8 4550.6

569.8 (3) 574.0 (2) 583.8 (4)

605.0 (2) 629.5 (8) 910.7 (6)

1079.7 (4)

1088.0 (3)

1102.8 1107.5 1140.4 1157.9 1167.3

4337.0 (5) 4317.6 (3) 4301.0 (3)

4277.0 (6) 4272.6 (6) 4264.2 (6)

4260.1 (4) 4252.8 (3)

1381.0 (4) 1399.7 (4) 1416.4 (3)

1440.7 (9) 1445.0 (9) 1453.3 (6)

1457.2 (4) 1464.3 (6)

~re ~;ven in keV" the intensity ~1~

4380.8 (2) 4365.6 (4) 4341.8 (5)

1336.7 (3) 1351.9 (4) 1375.2 (5)

All en~r~i~

4499.2 (6) 4461.0 (4)

1217.9 (5) 1256.6 (6) 1320.8 (7)

(2) (6) (2) (3) (2)

5535.7 (5) 5188.1 (7) 5179.5 (2)

181.4 (3) 530.5 (8) 538.4 (2)

(4) (7) (3) (5) (4)

5609.4 (1) 5558.8 (1)

E,r(AEv)

108.1 (1) 158.8 (2)

Eox(zEo~)

(13) (12) (7) (7) (8)

i~ ~ r h i t r ~ r v

157 (21) 94 (l 1)

79 (15) 84 (16) 93 (21)

79 (12) 74 (9) 93 (10)

90 (9) 57 (8) 72 (12)

30 (6) 50 (7)

163 52 77 65 88

165 (8)

154 (8)

144 (5) 12 (3) 24 (4) ~)

168 (9) 54 (8) 36 (4)

7 (2) ~') 13 (3) 78 (4)

95 (3) ") 134 (4) ~)

l~,/ESv

E n = 2 keV

3

1

5+

I-- 32 )2 i 3 5+ 2,~,

,,L~-+

,,~,~+ ~,~-,~+ ~,~,~+

½+ ~+ ~+

1+ ,23+ ,25

2,2,2

5+

~,2,2

3

|

~-,~~-,~~-,~~,~,~+

~,~,~+ ½-,~½,~-,~+ ~+,~+,~+

~,~ ~,~

101 (14) 140 (14) 108 (12) 112(13) 112 (46) 114(47)

4365.2 (5) 4358.5 (4) 4340.4 (4) 4323.5(4) 4298.9 (11) 4294.8(11)

156(16) 73 (16)

49 (10) 131 (13)

4419.0 (7) 4403.2(4)

4283.0(4) 4276.4(8)

65 (9) 39 (8)

102 (9) 46 (8) 64(8)

4522.4 (5) 4483.3 (8)

4599.8 (3) 4581.7 (7) 4571.8 (5)

78 (8) 103 (18) 74 (18)

53 (9) 27 (6) 62 (8) b)

4650.7 (4) 4637.0 (6) 4631.8 (8)

88 (5) b)

5135.0 (2)

105 (12) 23 (10) 55 (6)

52 (5) 26 (5) 96 (6)

100 (4) 91 (7)

Iy/E~

5110.7 (7) 4828.0 (7) 4659.8 (5)

5169.6 (4) 5164.1 (22) 5156.2 (5)

5558.8 (4) 5208.0 (9) 5200.8 (3)

5631.8 (2) 5581.0(3)

E~,(AE~,)

E . = 24 keV

i.0(2) 1.3 (3)

0.7(3)

0.72 (15) 0.56 (10) 0.68 (11) 0.82(13) 0.7 (3)

0.7(1)

0.46 (11) 1.3 (3)

0.75 (9) 1.4(3) 1.4(2)

2.1 (2) 1.6 (3) 0.7 (2)

0.22 (7) 0.9 (2) 2.5 (3)

1.6 (1)

1.6 (2) 2.4(11) 0.65 (9)

0.13 (4) 0.50 (15) 0.81 (7)

0.95 (5) 1.5(1)

~ 3 2t - ,23

t 3 5+ ~,2,2 i 3 2,2

I 3 5+ 2~2)2

l+ 3+ 5+ l+ 3+ 5+ I 3 5+ 2,2,2 I ~.,2 3 5+ 2,

21+ , 23+ , 25+

21+,23+ ,25+

t 3

21+, 23+ ,25+ t 3 2,2 t 3 2,2

21+, 23+ ,~5+

~-, 3-

2I - ,235I 3 3+ 2)2)2 1 3 21- ,23-

21+,23+ ,25 2l+ ,23+ ,~5+ 21-, 2 32t - ,2321+ , 23+ , 2S+

2 keV/24 keV

e~ .....

196

E. Kaerts et al. / 165Dy

The A R C results are summarised in table 3. The excitation energies in the first c o l u m n are calculated from the neutron binding energy in *65Dy (B, = 5715.76 keV), the n e u t r o n energy ( E , = 2 or 24 keV) and the primary transition energies. The reduced intensity scales for the reduced intensities in the 3rd and the 6th columns are arbitrary. Unlike thermal neutron capture, where only s-wave capture occurs, 2 keV and 24 keV neutrons lead both to s- and p-wave capture. For 2 keV neutrons, p-wave capture contributes only 5% while for 24 keV neutrons, the relative importance o f both processes is almost the same 30). Table 4 gives the spin and parity ( I ~) values o f the levels which can be fed via E l , M1 and E2 primary transitions after s- and p-wave capture in 164Dy ( I " = 0+). s-wave capture (1, = 0) results in a capture state with I 7 = ½+ from which I = = ½ , 3 states will be p o p u l a t e d more strongly (via E1 primaries) than I TM = 2l+ , ~3+ states (via M1 or E2 primaries). I ~ =~5+ levels on the other h a n d will only be p o p u l a t e d weakly since they can only be reached via E2 transitions, p-wave capture (l, = 1) can result in capture states with I~r = ½-, 3- . The positive-parity states can n o w be p o p u l a t e d via E1 primaries with the feeding of the I T = 25+ states being half as intense as for the I = =2~+, 23+ states while the negative-parity states can only be reached via the weaker M1 or E2 primaries. Figs. 4 and 5 give respectively the histograms o f the reduced intensities IR(2 keV) after 2 keV A R C and o f the ratio R of the reduced intensities after 2 keV A R C to the reduced intensities after 24 keV A R C ; R = IR(2 keV)/IR(24 keV). From these figures it is clear that, despite the averaging, the P o r t e r - T h o m a s fluctuations are still present. This results mainly from the relative low n u m b e r o f resonances which take part in the averaging after s-wave capture in 164Dy. Indeed, according to ref. 31), the m e a n distance between two ,TTr =~1 + resonances in the vicinity o f the neutron binding energy in 165Dy a m o u n t s 147 + 9 eV. Empirically, it is a n y h o w possible to distinguish in fig. 4 three g r o u p s o f reduced intensities with central values 160, 80 and 54. Taking into a c c o u n t statistical fluctuations o f +60% one gets the empirical classification o f I ~ values after 2 keV A R C as given in table 5. The accordingly assigned I " values are listed in the fourth c o l u m n o f table 3. D u e to the increasing i m p o r t a n c e o f p-wave capture in the 24 keV A R C experiment, I ~ =~+ and ~3+ (1

TABLE 4 Population of I ~<~ levels in 165Dy after s- and p-wave neutron capture in l~Dy ( I ~ = 0 +) s-wave capture

1-

,~3 ,~3 + ~+

1+

25

p-wave capture

tc~ _-1 +:

1~"=~-

I~ =~-

E1 M1, E2 E2

M1, E2 E1

-

E2

M1, E2 E1 E1 M1, E 2

E, Kaerts et al. / t6SDy

197

N 10

5

sb

~bo 19 1/2+ 31/2+

5/2-"--~ , I " ~ / 2 +

L

It

2~0 k V 5 • 1 13,(2 • )IE 7

1/2-,3/2-

Fig. 4. Histogram of the reduced intensities after 2 keV ARC in 164Dy.

LI oL~ 5/2-~

I~

~o

' I ,,,,--z1/2+,3/2 +" 5/2"~

t

1~ - I

1/2-,3/2-

F-l it

2~0 IR (2keY) -I IR (2t, keV)

Fig. 5. Histogram of the ratio R of the reduced intensities after 2 keV A R C to the reduced intensities after 24 keV A R C in ~64Dy.

a n d 3-) levels will be p o p u l a t e d relative m o r e s t r o n g l y ( w e a k l y ) in the 24 keV A R C e x p e r i m e n t t h a n in the 2 keV A R C e x p e r i m e n t . As a result, the ratio R gives a s t r o n g i n d i c a t i o n for the p a r i t y o f a n I -- ½, 3 state. Besides, the lowest R - v a l u e s are e x p e c t e d to o c c u r for p r i m a r y t r a n s i t i o n s w h i c h p o p u l a t e I ~ = 25- levels. A m o r e q u a n t i t a t i v e I '~ classification on the b a s i s o f the R - v a l u e s is given in the last c o l u m n o f t a b l e 5. T h e a s s i g n e d I '~ v a l u e s a r e listed in the last c o l u m n o f t a b l e 3.

E. Kaerts et al. / 165Dy

198

TABLE 5 Empirical classification of I = values 1= 1 I+

3-,2 3+

,~ 5+ 2 5

a)

I R -_

lw (2 keY) ") 64-256

32-128 22-86 <22

R b) 1-2

0.7-1.2 0.3-0.8 <0.3

I~,/E~,.5

b) R = IR(2 keV)/IR(24 keV).

4. The low-energy level scheme of 16SDy 4.1. C O N S T R U C T I O N OF THE LEVEL SCHEME

Starting from an existing level scheme of 165Dy [ref. 3)] and the secondary y-transitions from table 2, partial decay schemes for the previously known levels below 1.5 MeV [ref. ~2)], the levels from table 1 below 1.5 MeV and the levels from table 3 were built. In a next step, the sum of the squares of the deviations between y-transition energies and the corresponding level energy differences were minimised with a least squares fit procedure. Only those y-transitions for which the deviations mentioned above are smaller than 2.2 times the error were assumed to be well placed. Only the levels at 164.6, 1351.9 and 1453.3 keV from table 3 could not be confirmed by this method. Finally, the remaining secondary y-transitions were used to iocalise some new levels after which the least squares procedure was repeated. In this way, a rather detailed and at the same time reliable level scheme for 165Dy has been established. It consists of 50 levels below 1500keV and 317 secondary y-transitions. From this level scheme and the primary transitions the neutron separation energy in 165Dy was found to be 5715.76 (30) keV (total error given). The complete level scheme is given in table 6. Both the search for new levels and the construction of the decay schemes were mainly based on the Ritz combination principle. Since the secondary y-transitions were measured very precisely (see table 2), this method could be used with sufficient confidence for excitation energies below 1.5 MeV. Below this energy, only 6 double placements occur (only 1 below 800 keV). Above 1.5 MeV, the number of accidental Ritz combinations rapidly increases.

4.2. SPIN A N D PARITY ( I ~) A S S I G N M E N T S

For most levels, the I ~ assignments were initially based on the ARC results and further limited by the decay schemes in table 6 and occasionally by the multipolarity measurements of Dutta et al. 9). Transitions with unknown multipolarities were

E. Kaerts et al. / 165Dy

199

TABLE 6 Decay schemes and I = assignments of levels in t65Dy below 1500 keV

i = b)

E~(AE,) a) (keV)

83.396 (2) 108.155 (2) 158.589 (2) 180.923 (2) 184.254(2) 186.095 (3)

_9+ 2 !2 3~35IA+ 2

261.770 (2)

37 -

297.683 (2)

_72

337.163 (2) 360.630 (2)

992

533.492(2)

5_ 2

83.398 (2) 108.157 (3) 50.434 (1) 72.768 (1) 184.252 (2) 186.100 (6) 102.701 (2) 261.771 (2) 178.374 (4) 77.514(1) 139.096 (2) 116.760(1) 156.240 (1) 277.238 (11) 174.554 (6) 176.367 (5) 98.863 (2) 533.494 (9) 425.335 (16) 374.903 (2) 352.574 (2) 235.796 (12) 349.241 (2) 271.721 (1) 538.634 (3) 430.478 (5) 380.045 (1) 357.714 (3) 354.381 (1) 462.103 (3) 411.679 (2) 386.011 (2) 465.427 (3) 414.997 (3) 392.663 (2) 311.812(3) 583.994 (4) 500.603 (7) 403.073 (1) 286.312 (2) 399.746 (3) 322.224 (2)

Ex(aEx) ") (keV)

Final state

y-transition

Initial state

538.634 (2)

33 +

570.265 (2)

I 3 -(3,3)

573.584 (2)

I 3 -(~, ~)

583.996 (2)

5+

iv c) 454 2468 3864 327 18895 16 33 155 119 202 970 524 242 10 1 13 58 344 164 163 200 25 1881 424 9331 567 571 321 428 224 4931 4396 5153 4358 1390 30 3100 1453 395 100 243 36

N

d)

2 5 1 1 11 9 7 17 9 2 8 3 8 11 n 2 9 7 8n 16 15 16 12 17 14 7 17 17 19 17 18 n 17 17 17 17 19 11 d 11 7 18 14 16 9

Ex(aEx) (keV)

1.

0.000 0.000 108.155 108.155 0.000 0.000 83.396 0.000 83.396 184.254 158.589 180.923 180.923 83.396 186.095 184.254 261.770 0.000 108.155 158.589 180.923 297.683 184.254 261.770 0.000 108.155 158.589 180.923 184.254 108.155 158.589 184.254 108.155 158.589 180.923 261.770 0.000 83.396 180.923 297.683 184.254 261.770

~+ ~+ ½~~+ ~+ 3+ ~+ ~+ ~~~3+ H+ 2 ~~~+ ~2~5~+ ½~~~½12~11~~+ ~+ ~~~~-

200

E. Kaerts et al. / 165Dy TABLE 6--continued Initial state

),-transition

E~(aEx) ~) (keV)

i ~ b)

605.092 (2)

~-

607.624 (2)

5 7(~,~)

628.837 (2)

I-

648.972 (3)

~+

657.996 (2)

702.892 (8)

705.911 (3)

2-

(~-~)7 9 + (~, ~) ~-,~

Final state

E~(aE,) ~) (keV)

iv c)

N d)

Ex(~E~) (keV)

496.942 (3) 446.506(8) 424.161 (8) 420.840 (3) 343.323 (3) 449.027 (9) 426.696 (9) 309.941 (2) 270.461 (4) 423.366 (6) 345.849 (3) 246.997 (2) 520.679 (6) 470.251 (4) 447.915 (2) 331.151 (10) 444.564 (8) 90.208 (2) 648.962 (5) 565.578 (3) 462.883 (7) 464.610 (63) 387.207 (4) 351.283 (5) 311.812 (3) 110.328 (7) 64.968 (5) 549.811 (27) 499.407 (4) 477.072 (3) 473.737 (3) 396.222 (3) 297.370(3) 52.906 (1) 441.120 (19) 342.269 (10) 365.724 (7) 524.983 (4) 408.229 (3) 368.749 (2) 444.139(8) 121.898 (10)

6029 31 32 1277 464 10 47 25 12 113 105 46 25 1262 2454 548 5 2 271 495 84 20 46 29 30 5 14 10 1915 2044 219 295 52 41 12 5 6 176 289 177 15 7

16 5n 8n 16 14 4n 11 n 13 n 8 16 14 5 4n 15 7 11 4n 5 8 5 14 n 3n 11 n 7n 11 d 2 1 1n 16 15 14 n 18 14 1 4n 3n 3n 8n 17 n 9 5 2

108.155 158.589 180.923 184.254 261.770 158.589 180.923 297.683 337.163 184.254 261.770 360.630 108.155 158.589 180.923 297.683 184.254 538.634 0.000 83.396 186.095 184.254 261.770 297.683 337.163 538.634 583.996 108.155 158.589 180.923 184.254 261.770 360.630 605.092 261.770 360.630 337.163 180.923 297.683 337.163 261.770 583.996

½~~~~~~32~3~11~1~+ ~+ 3+ L~+ 2 2~~9-

~+ I+ ½~~5-

~32~9--

31~3~I÷

E. Kaerts et al. / 165Dy

201

TABLE 6---continued

Initial state

y-transition

Ex(aEx) a) (keV)

i ~ b)

737.855 (3)

(I, 5)-

911.968 (4)

976.766(22)

(L ~) +

1016.070 (3)

5+

1080.037 (3)

(~, ~)

1088.007 (3)

1

3

3 --

-

Final state

E~(AE~) ~) (keV)

l e)

N d)

Ex(AE~)

i ~-

556.938 (6) 440.169 (13) 400.682 (4) 377.221 (6) 132.767 (5) 79.866 (4) 911.966 (4) 828.569 (17) 378.487 (4) 976.662 (194) 893.421 (9) 790.581(50) 64.757 (12) 1016.100 (15) 932.657 (11) 831.822 (9) 754.298 (8) 482.591 (6) 408.453 (6) 442.548 (41) 432.083 (6) 367.094 (4) 104.104 (2) 971.853 (34) 921.442 (22) 546.543 (2) 541.402 (5) 509.772 (6) 474.945 (3) 506.459 (4) 451.205 (3) 979.834 (21) 929.399 (11) 907.096 (18) 903.736 (19) 554.521 (11) 549.371 (3) 504.013 (6) 517.771 (11) 514.426 (5) 459.168 (5)

310 55 29 15 2 11 3175 90 61 137 296 11 6 1038 684 376 222 49 36 8 45 23 57 46 136 392 227 47 383 828 76 995 466 141 128 20 253 201 10 192 45

10 12 n 6n 3n 3n 1 7 5 15 1 6 1 1 6 7 9 6 8 3 3 7 5 5 2 2 8 7 4 15 8 4 8 7 3 4 5 11 7 3 6 10

180.923 297.683 337.163 360.630 605.092 657.996 0.000 83.396 533.492 0.000 83.396 186.095 911.968 0.000 83.396 184.254 261.770 533.492 607.624 573.584 583.996 648.972 911.968 108.155 158.589 533.492 538.634 570.265 605.092 573.584 628.837 108.155 158.589 180.923 184.254 533.492 538.634 583.996 570.265 573.584 628.837

15~~115+ ~+ 15+ ~+ lj+ 2 ~+ 5÷ ~+ 151(~,~)5 7(~,~)l 3 ~+ 5+ ~+

(keV)

~~~+ (~,~)t 31(~,~)l 31½1111I+ I+ (~,~)t 3(~,~)l 3~-

E. Kaerts et al. / 165Dy

202

TABLE 6 - - c o n t i n u e d

Initial state

y-transition

Ex(~Ex) a) (keV)

i ~ b)

1103.042 (3)

3-

1108.198 (3)

1135.814 (4)

1140.863 (4)

E~(~E~)a)

ivc)

N ~)

1363 823 202 17 163 25 824 6 468 131 10 241 194 734 88 111 58 43 824 455 114 11 445 202 14 24 490 425 110 52 127 55 88 39 31 6 48 611 37 600 736 31 9

7 7 3

(keV)

(~,~) 3 5÷

~

(~,~) i 3 +

994.870 (8) 944.433 (7) 922.113 (13) 805.320 (47) 918.803 (14) 841.384 (47) 569.566 (6) 495.429 (12) 564.409 (2) 519.054(4) 532.748 (23) 529.451 (14) 474.212 (4) 1108.204(13) 949.622 (21) 927.222 (31) 923.957 (62) 574.705 (6) 569.566 (6) 524.202 (2) 537.988 (34) 450.213 (12) 534.617 (4) 479.372 (4) 196.231 (10) 1027.802 (148) 977.184(47) 954.865 (11) 838.162 (25) 951.596 (50) 597.167 (8) 551.814 (5) 486.841 (6) 562.227 (5) 506.980 (15) 397.962 (9) 1032.816 (54) 982.257 (24) 602.244 (8) 570.604 (6) 535.767 (3) 512.002 (45) 228.922 (21)

Final state

(1) 4

(1) 9d 2 11 6 2 8 12 7 4 3 1

8 9d 8 2d 3 8 14 6d 2 6 6 3 2 6 6 9 6 2 3 3 8 5 9 5 1

3d

Ex(AEx) (keV) 108.155 158.589 180.923 297.683 184.254 261.770 533.492 607.624 538.634 583.996 570.265 573.584 628.837 0.000 158.589 180.923 184.254 533.492 538.634 583.996 570.265 657.996 573.584 628.837 911.968 108.155 158.589 180.923 297.683 184.254 538.634 583.996 648.972 573.584 628.837 737.855 108.155 158.589 538.634 570.265 605.092 628.837 911.968

!2 32 _52

72

72 5 2 5 7 (~, ~)

3+ 2 5+ 2

(~, ~) 1

3

-

1

3

-

5 2 7+ 2

32 5-

52 3+ 2 5+ 2

(~, ~)

-

(~,1 ~)

-

1

3

3

52 5+ 2

32

_7-2 52 3+ 2

5_+ 2 7+ 2

55

7 (~, ~) 12

(~, ~) 1

3

52 5+ 2

-

E. Kaerts et al. / 165Dy

203

TABLE 6---continued

Initial state

E,,(AE,,) a)

y-transition

i ~ b)

(keV) 1158.116 (3)

1166.893 (4)

1174.953 (3)

1218.350 (4)

1256.498 (6)

Ez,(AE.e ) a) (keV)

5+

a+2

2

5+

!2,2~

Final state

1158.083 (31) 1074.746 (50) 619.480 (10) 574.122 (3) 509.139 (7) 584.524 (17) 529.282 (4) 452.208 (4) 553.002 (10) 420.395 (50) 1008.272 (17) 596.626 (3) 561.794 (4) 508.899 (3) 593.282 (12) 537.988 (34) 1016.530 (80) 994.012 (26) 990.673 (25) 641.441 (15) 567.318 (13) 636.410 (42) 590.963 (14) 601.366 (6) 546.123 (6) 469.045 (4) 437.090(6) 86.930 (6) 920.666(11) 644.768 (11) 589.490(13) 512.448 (5) 610.793 (35) 613.259 (3) 560.352 (7) 480.491 (5) 130.370 (20) 1072.212 (9) 717.804 (36) 672.904 (194) 686.293 (42) 651.434(32) 598.560 (33)

I:, c)

N d)

Ex(aEx ) (keY)

336 111 185 156 125 79 76 57 36 25 310 623 53 852 28 114 175 291 161 27 39 43 65 44 67 157 16 5 289 31 22 43 10 367 19 192 18 1680 39 18 15 46 6

4 3 8 10 5 5 2 10 5 2 5 9 7 8 6 2d 1 6 6 5 4 2 8 6 4 14 4 2 5 5 3 4 1 9 5 1 2 8? 5 (1) ? 2 3 1

0.000 83.396 538.634 583.996 648.972 573.584 628.837 705.911 605.092 737.855 158.589 570.265 605.092 657.996 573.584 628.837 158.589 180.923 184.254 533.492 607.624 538.634 583.996 573.584 628.837 705.911 737.855 1088.007 297.683 573.584 628.837 705.911 607.624 605.092 657.996 737.855 1088.007 184.254 538.634 583.996 570.265 605.092 657.996

7+ 2 9+ 3+ _5+ 2 7+ 2

(~,~)5-

_5- _7 2 ~2 32 5 7 -

(~,~) 3_2

(~,9 I

3

--

352

(~,~) I

3

-

_5 2 3-5--

52 5 7 (~, ~)

3+ 2 5+

(~,9 I

3

5--

-

7

(~,~) 5

7 --

3_2

22 I

3

-

(~,~1 5-2

5

2

2

,2

5 7 (~, ~) 2

(L ~)2 52

5+ 2

(½,~)32 5-

E. Kaerts et al. / 1~SDy

204

TABLE 6---continued

Ex(~Ex) a) (keY)

i ~ b)

1309.296 (4)

5-

1320.806 (9) u

1337.091 (6)

1376.334 (5)

1380.881 (11)

1400.269 (4)

Final state

y-transition

Initial state

2

1 3 + (~,~)

~+ 2

5+

3 5 + (~,~)

Ev(aE~) ~) (keY)

Iv c)

1201.148 (112) 1150.547 (83) 1128.402 (102) 1125.032 (20) 1047.518(32) 704.291 (41) 1212.511 (211) 1161.826 (100) 1139.769 (81) 1136.433 (38) 212.611 (12) 64.312 (6) 1228.935 (50) 1178.458 (36) 257.052 (22) 249.082 (6) 234.065 (6) 228.922 (21) 196.231 (10) 1268.133 (33) 1217.720 (53) 1195.438 (166) 1192.177 (67) 837.710 (22) 792.385 (20) 718.210 (69) 360.278 (6) 296.293 (3) 1222.319 (56) 1199.973 (91) 1083.175 (15) 847.436 (86) 842.144 (57) 731.871 (23) 775.705 (42) 807.344 (91) 674.867 (94) 292.893 (10) 277.843 (5) 1292.028(42) 1241.637 (36) 1219.225 (33) 826.646 (27)

41 32 55 288 477 13 34 57 27 60 1 8 163 1020 7 7 5 9 14 233 152 207 72 227 22 22 13 11 212 66 392 18 30 39 18 25 20 3 5 715 316 253 27

N a) 2 3 (2) 5 8 2 (2) 2? 2 3? 3 1 3 6 14 5 12 3d 6d 4 2 4 2 11 5 3 3 9 3 2 4 1 (1) 4 1 3 3 5 2 3 7 3? 5

Ex(~E~) (keV) 108.155 158.589 180.923 184.254 261.770 605.092 108.155 158.589 180.923 184.254 1108.198 1256.498 108.155 158.589 1080.037 1088.007 1103.042 1108.198 1140.863 108.155 158.589 180.923 184.254 538.634 583.996 657.996 1016.070 1080.037 158.589 180.923 297.683 533.492 538.634 648.972 605.092 573.584 705.911 1088.007 1103.042 108.155 158.589 180.923 573.584

½ ~~27-

~½2(~,3~)5+ 2! ~ 2 ~~(~,l i)32(~,3~)5+ 1 3 + (~,~) ½~~~+ ~+ 2+ (~,l ~)33-

~~~~+ ~+

(~, t ~) 3~5- ,~7 ~~½-

(~,t ~)3-

E. Kaerts et al. /

t:':Dy

205

TABLE 6--continued

Initial state

y-transition

E,~(AE,,) a) (keV)

i ~ b)

Ev(~E~) a) (keV)

1400.269 (4)

(~,~) 3 5÷

1416.334 (3)

i 3 5+ ~,3,~

816.272 (14) 795.304 (62) 742.264 (15) 320.236 (3) 1257.683 (46) 882.833 (13) 846.058 (7) 811.248 (11) 842.734 (27) 336.299 (4) 328.328 (2) 313.293 (2) 258.217 (6) 1142.732 (80) 1256.102 (90) 856.526 (22) 791.342 (59) 131.145 (22) 1260.531 (19) 1182.982 (46) 906.066 (20) 860.611 (37) 871.089 (33) 303.890 (66) 277.743 (42) 1297.865 (36) 1275.421 (119) 1272.550 (239) 886.092 (29) 851.382 (52) 798.398 (7) 882.833 (13) 827.565 (43) 872.398 (11) 848.898 (110) 368.352 (14) 1280.628 (37) 1203.187 (61) 931.351 (10) 926.187 (11) 880.839 (22) 891.319 (25) 835.987 (23)

1440.458 (42) u

~+

1444.726 (18) u

3- , ~5+

1456.390 (9)

1464.844(4)

~2

~-

88 14 37 15 343 124 240 165 61 60 63 36 3 43 226 79 28 5 612 180 467 130 27 11 7 296 122 108 100 44 342 124 40 169 32 15 180 155 488 330 39 148 42

Final state N d)

E~(AE~) (keV)

3 2 6 7 4 3d 9 5 4 13 4 10 8 3 2 2 5 2 6 2 6 5 2 2 2 3 2 3 4 1 9 3d 3 5 2 3 4 2 8 6 2 5 4

583.996 605.092 657.996 1080.037 158.589 533.492 570.265 605.092 573.584 1080.037 1088.007 1103.042 1158.116 297.683 184.254 583.996 648.972 1309.296 184.254 261.770 538.634 583.996 573.584 1140.863 1166.893 158.589 180.923 184.254 570.265 605.092 657.996 573.584 628.837 583.996 607.624 1088.007 184.254 261.770 533.492 538.634 583.996 573.584 628.837

~+ ~~(~,l 3)33~(3,t 3)3 ~(~,l 3)3(~,3)1 3 ~~~+ 3~~+ ~+ ~~+ ~+ (3,! ~)3-(3,13)3+ ~+ ~2 ~~(3,13)3~(~,l ~)3~~+ (3,5~)7~~3+

~÷ (~,l 3)3~-

E. Kaerts et al. / 16SDy

206

TABLE 6---continued

Ex(aEx) ") (keY) 1464.844 (4)

I " b)

E~,(AE~,) ") (keV)

3 2

1479.111 (8)

3 5 (~, ~)

1482.060 (7)

52

5715.767 (15)

Final state

y-transition

Initial state

½+

384.813 (4) 376.832 (4) 356.659 (5) 329.041 (16) 323.994 ( 11 ) 306.733 ( 11 ) 208.339 (4) 155.547 (3) 127.719 (1) 1370.916 (32) 1320.446 (39) 1181.315 (59) 945.815 (121) 905.527 (14) 850.288 (12) 391.120 (4) 376.088 (2) 1373.530 (172) 1323.437 (84) 1301.342 (95) 1184.307 (34) 1220.317 (71) 1121.565 (130) 943.548 (104) 833.039 (40) 101.175(1) 4250.883 (51) 4270.945 (87) 4275.305 (50) 4315.461 (45) 4334.848 (88) 4339.504 (46) 4459.316 (50) 4497.515 (63) 4548.957 (37) 4557.625 (51) 4575.062 (157) 4607.645 (44) 4612.730 (45) 4627.566 (550) 4699.785 (47) 4803.859 (50) 5110.695 (47)

iv c)

N d)

Ex(AEx) (keY)

11 20 54 5 1 19 18 2 2 275 211 148 37 277 116 27 64 58 148 96 211 98 82 37 72 6 124 27 116 150 47 119 208 88 141 35 6 225 789 2 43 27 906

5 9 16 6 2 16 11 2 2 3 3 2 2 5 5 8 13 2 2 2 3 2 3 2 6 5 1p 1p 1p 1p 1p 1p 1p 1p 1p 1p 1p 1p 1p 1p 1p 1p 1p

1080.037 1088.007 1108.198 1135.814 1140.863 1158.116 1256.498 1309.296 1337.091 108.155 158.589 297.683 533.492 573.584 628.837 1088.007 1103.042 108.155 158.589 180.923 297.683 261.770 360.630 538.634 648.972 1380.881 1464.844 1444.726 1440.458 1400.269 1380.881 1376.334 1256.498 1218.350 1166.893 1158.116 1140.863 1108.198 1103.042 1088.007 1016.070 911.968 605.092

(½,2)3-

(2, I) + I (½,2) + ~+ (~,1~)3 I(2, 2) ÷ ½25~(~,1~)31~~1I ~32+ 5+ I+ 1~,~3-5+ I+ (~, 3 ~) 5÷ I+ ~+ 3 (3,I ~) ~+ ~+ ~+ (~, t ~) 3+ (~, 3 ~) 5+ 22I+ ~+

E. Kaerts et al. / t65Dy

207

TABLE 6--continued Initial state Ex(AEO a) (keV)

y-transition I ~ b)

Ev( AEv ) a) (keV)

Iv

5142.223 (45) 5145.570 (44) 5177.148 (50) 5557.109 (60) 5607.504 (55)

1099 1234 894 4204 5143

Final state

~)

Ex(AEx ) (keV)

l ~"

N ~) 1p 1p 1p 1p 1p

573.584 570.265 538.634 158.589 108.155

(3,1~)3 (3,13)32+ ~~-

~) Absolute errors on level energies are given in eV. u - uncertain level. b) i ~ values are obtained from all the availABLE experimental information. No model-dependent arguments are used (see subsection 4.2). c) Photons per 105 neutron captures in ~64Dy. d) N designates the total number of independent observations of a given transition. d - double placement. n - transition placed for the first time in the level scheme below 800 keV. p - primary transition. ? - uncertain placement. a s s u m e d to be o f E l , M1 or E2 type. Levels b e l o w 1.4 MeV, which have n o t b e e n observed in the A R C m e a s u r e m e n t , m u s t have 1/> 5. This follows from the completeness g u a r a n t e e d by the A R C t e c h n i q u e . Below 740 keV, I '~ values for such levels were initially t a k e n from the N u c l e a r D a t a Sheets c o m p i l a t i o n of mass 165 [ref. 1~)]. I n most cases, the a s s i g n m e n t o f I ~ values is straightforward a n d therefore o n l y a few, less e v i d e n t a s s i g n m e n t s will be discussed in more detail. The A R C data in table 3 i n d i c a t e that the level at 1166.893 keV m u s t have spin ½ or 23while the level at 657.996 keV - b e c a u s e it has not b e e n observed in the A R C m e a s u r e m e n t - must have 1 i> I- Both levels are c o n n e c t e d via the i n t e n s e 508.899 keV y - t r a n s i t i o n . A c c o r d i n g to D u t t a et al. 9), the m u l t i p o l a r i t y of this t r a n s i t i o n is E1 fixing the I "~ values o f b o t h levels: I'~(657.996) = I - a n d I'~(1166.893) = 23+. I n d e e d , I'~(657.996) = ~+ is e x c l u d e d b y the decay scheme o f this level. F r o m the six p r o p o s e d decay lines o f the 1256.498 keV level, o n l y the 1072.212 keV t r a n s i t i o n to the I ~ = I - level at 184.254 keV has a large y-intensity. The e x p e r i m e n t a l v a l u e is 3.5 times higher t h a n the o n e r e p o r t e d in ref. 3) a n d c o n s e q u e n t l y , the t~K v a l u e from D u t t a et al. 9) is r e d u c e d with the same factor: aK = 0.0028 (8). This agrees with the theoretical values for M1 (aK = 0.0039) a n d E2 (aK = 0.0022) radiation. The p l a c e m e n t o f the 1072.212 keV line therefore implies z r ( 1 2 5 6 . 4 9 8 ) = - . This is i n c o n t r a d i c t i o n with the 2 keV A R C results. Because the 1072.212 keV t r a n s i t i o n does n o t fit p r o p e r l y b e t w e e n the 1256.498 keV a n d the 184.254 keV levels, we have t a k e n I ( 1 2 5 6 . 4 9 8 ) = ½, 23. F i n a l l y , the a d o p t e d I~(1158.116) = ~+ a s s i g n m e n t - which follows u n a m b i g u o u s l y from the d e c a y p a t t e r n o f this level - is o n l y c o n s i s t e n t with the 2 keV A R C results.

208

E. Kaerts et al. / 165Dy

4.3. COMPARISON WITH PREVIOUS RESULTS Previously, the decay schemes and I = assignments for 165Dy levels below 800 keV have already been described extensively [ref. 11) and the references mentioned therein]. Our work reproduces these results quite well. Moreover, some 25 new y-lines could be placed in the level scheme below 800 keV. In table 6 these lines are denoted with a " n " . Also more definite I ~ assignments could be made for a large number of levels. Finally, the discrepancy which arose previously when the 7+ member of the rotational band based on the 3+,538.6 keV exact energy of the ~ level was calculated on one hand from the transitions within the rotational band sequence (110.345 keV) and on the other hand from the transitions going to the ground state rotational band (462.23, 565.16 and 649.0keV) [ref. 4)] could be eliminated by resolving the closely spaced doublet 462.103 (5)/462.883 (7) keV and the triplet 564.409 (2)/565.578 (3)/565.718 (9) keV. There are also a few points of difference. The two levels at 480.07 and 520.49 keV for instance [ref. i1)] could not be confirmed. Each of these levels was defined by only two decaying transitions. In the present study, these y-transitions have not been observed (183.32 and 218.29 keV) or could not be assigned to 165Dy (119.41 and 222.80 keV). Markus et al. 4) presented the first decay scheme for the level at 1103.042 keV. On the basis of coincidence measurements, the 569.82 keV transition from Schult et al. 3) was placed between the 1103.042 and the 533.492 keV levels. The GAMS data however show that this transition has a multiplet structure of which only the 569.566 (6)keV component fits between both levels. According to table 6, the 569.566(6) transition can also be placed between the levels at l108.198keV and 538.634 keV. Moreover, the intensity of this transition is in agreement with this placement. With I, K~(1108.198)= 3, 3+ (see table 7), the theoretical relative transition intensities for the 569.566 and the 524.202 keV lines (assumed to be M1) to the I =3_ and ~ _5 members of the K ~=3+ ~ band at 538.634 keV are, respectively, 1.00 and 0.52. The experimental values are respectively 1.00 and 0.55 (2). Consequently, we expect that - if the 569.566 keV transition has a doublet structure - the largest part of its intensity originates from the deexcitation of the level at 1108.198 keV. Unfortunately, Markus et al. 4) have not listed the intensity of their coincident 1103.042~ 533.492 keV transition.

5. The rotational band structure in 165Dy According to Lamm 32), the nuclear mass distribution of ~65Dy is characterised by the deformation parameters e2 = 0.267 and e4 = 0.009 or by a 6-value 33): 6 = 0.946{1.06e2 + 0.2e22 - 1.8e2e4}

(3)

of 0.28. Therefore, 16SOy is expected to possess a pronounced rotational band

A

11.02 9.56 9.98 9.48 10.56 8.59

9.30 10.58 11.03 10.58 9.17 11.04 11.03 9.26

(keV)

1.45

-0.08

-0.30

0.04

0.58

a

0.0 108.155 184.254 533.492 538.634 570.265 573.584 911.968 1016.070 1080.037 1088.007 1108.198 1140.863 1256.498 1337.091 1376.334

(keV)

E(I=K)

1103.042 1135.814 1158.116 1166.893 1309.296 1400.269

83.396 158.589 261.770 607.624 583.996 605.092 628.837 976.766

(keV)

E(I=K+I)

1380.881

1218.350

1174.953

186.095 180.923 360.630 702.892 648.972 657.996 705.911 1054.0"

(keV)

E(I=K+2)

737.855

303.3* 297.683 480.07*

(keV)

E(I=K+3)

1283.0"

337.163

(keV)

E(I=K+4)

520.49*

(keV)

E(I=K+5)

* Only observed in the 164Dy(d, p)165Dy reaction [ref. 7)]. a) These Nilsson assignments are only added for information; they were not used for establishing these band structures.

3+

1+

3-

l+

3+

3-

1-

~+

5+

3

1

3+

~-2

5-

½-

7+

K~

TABLE 7 Experimental band structure in 165Dy below 1.4 MeV

½-{~-[521],2 +} ~-{½-[521],2 +} 5+[651] ½+{~-[512],2-} ~-{~-[514], 2+}+~-[512] ~+[651]+½+{~-[523], 2-}

~+[633] ½-[521] ~-[512] ~-[523] +~-{~-[521], 2 ÷} ~÷{~+[633],2 ÷} ½-{~-[512], 2+} +½-[510] ~-[521] +~-{½-[521], 2 ÷} ~+[642]

Assigned Nilsson configurations a)

""

~"

2

-

7/2 - 7 / 2 * [633]

9/2 -

11/2

5 / 2 - 3 / 2 - (7/2*[633] 2*)

7 / 2 - -

1/2

5/2 3/2 1/2

[521]

[521]

9/2 7/2

[521]-2

(1/2

+3/2

5/2 3/2

+ )

5/2

5/2

7/2

9/2

[5121

[510]

+(1/2

[521]

3/2-[521]

+ 1/2

3 / 2 - [523]

7 / 2 - 5 / 2 - -

5/2 (5/2-[512]- 2*) 5/2

7/2

9/2 . . . .

3/2 1 / 2 - -

5/2

7/2

2*)

1521]- 2 + )

3 / 2 _ _ 1 / 2 - -

5/2

(3/2

5/2+[642]

5/2

7/2 . . . . Kw

5/2

_ 5/2 +

3 / 2 ÷ [651 ]

3 / 2 - -

6/2 (5/2

5/2 3/2 1/2 [512]-2

)

(7/2 [514]-2]*) + 3/2-[512]

3/2

5/2

-

( 5 / 2 - [523] - 2 - )

1/2+[651]+

3/2 1/2 -

5/2

Fig. 6. Rotational bands i n 165Dy below 1.4 MeV. Only the dominant configurations and restricted I " values are given. The I ~ = 3+ level at 1376.334 keV has been omitted.

0.0

0.5

1.0

E(MeV)

E. Kaerts et al./ t65Dy

211

structure. The grouping of the nuclear levels into rotational bands was based on the following assumptions: (i) The excitation energy E(I, K) of a rotational state with spin I relative to the band head ( I = K ) can be written as:

E(I,K)-E(K,K)=A{I(I+I)-K(K+I)+~K.I/2[(-)'+J/2(I+½)+I]a},

(4)

with A the rotational parameter and a the decoupling parameter. A-values are expected to lay around 10 keV. (ii) Levels belonging to the same rotational band show a similar decay pattern. (iii) The level scheme below 1.4 MeV is complete for I =½ and I =3 levels of both parities. Together with the experimental values for the rotational parameter A and the decoupling parameter a (if K =½), the arrangement of the low-lying levels (Ex < 1.4 MeV) into rotational bands is given in table 7. A graphical representation of the rotational band structure in 165Dybelow 1.4 MeV is given in fig. 6 where - in order to avoid an overcomplication of the figure - only restricted I ~ values are given.

6. The intrinsic level structure in 16SDy It is well known that in deformed nuclei each intrinsic state gives rise to a rotational band. After having studied this rotational band structure in ~65Dy, we shall now give a detailed description of its intrinsic structure in terms of both one-quasiparticle excitations and collective vibrational excitations. Before we start with the interpretation of the experimental results, some theoretical considerations concerning the one-quasiparticle spectrum in 165Dy and the influence of the quasiparticle-phonon interaction will be given. 6.1. SOME THEORETICAL CALCULATIONSAND CONSIDERATIONS

6.1.1. One-quasiparticle excitations in ~65Dy. The theoretical one-quasiparticle spectrum in 165Dy (Z = 66, N = 99) was calculated in the particle-rotor model with inclusion of pair correlations. The model is fairly standard and is described extensively in reference 34) and in the references mentioned therein. The particles are assumed to move independently in a deformed harmonic-oscillator potential of modified Nilsson type 35,32). The potential parameters were taken from the systematics in the rare earth region: K = 0.0637 and /x = 0.437 [ref. 34)]. The deformation parameters e2 = 0.267 and E4 = 0.009 were taken from reference 32). In first instance, the energies and wave functions of the lowest lying Nilsson states in 165Dy were calculated. They are given in tables 8 and 9. The energies are expressed in terms of htoo=7.63 MeV and the Nilsson states K~[Nn~A] are expressed in the coupled representation of spherical oscillator basis states qbNij: K ~[Nn=A] = E C)I(N, K) qbNtj, jl

(5)

E. Kaerts et al. / 165Dy

212

TABLE 8 Energies and wave functions for some negative-parity Nilsson states in 16SDy

K[Nn~A]

E(hm o)

½[530] ~[532] ~[521] ~[532] ½1521] I[512] ~[514] ½1510] ~[512]

6.192 6.229 6.393 6.461 6.595 6.651 6.736 6.941 6.968

Ct/2,1

C3/2,,

C5/2,3

C7/2,3

C9/2,5

Cu/2,5

0.020

0.333 -0.237 0.259

0.519

0.277

0.345 0.417 0.094 0.263 0.439 -0.050

-0.044

0.657 -0.342

0.489 -0.470 0.697 -0.400 0.452 0.859 -0.271 -0.385 0.309

0.684 0.682 0.615 0.851 -0.482 0.470 0.951 -0.297 -0.363

-0.250 0.289 -0.244 0.216 -0.155 -0.199 0.147 0.091 -0.083

0.568 0.805

TABLE 9 Energies and wave functions for some positive-parity Nilsson states in 165Dy

K[Nn~A]

E(ho~o)

C1/2.o

C3/2,2

C5/2, 2

C7/2. 4

C9/2. 4

~[400] ~[402] ½[660] ~[651] ~[642] ~[633] ~[624] ~[615] ~[606]

6.180 6.203 6.252 6.310 6.419 6.572 6.766 6.999 7.272

0.774

0.514 0.933 -0.016 -0.014

-0.303 0.233 0.133 0.092 0.044

-0.201 -0.269 -0.018 -0.035 -0.034 -0.021

0.064 -0.058 0.412 0.374 0.310 0.228 0.134

0.031

Cll/2.6

C13/2,6

-0.020 -0.054 -0.076 -0.088 -0.088 -0.072

0.900 0.920 0.946 0.969 0.987 0.997 1.000

with C~l the expansion coefficients. In a next step, the effects of pair correlations were taken into account by solving the Bardeen-Cooper-Schrieffer equations with consideration of the blocking effect. This yields for each single-particle state v occupied by the uncoupled neutron, the Fermi surface A~ and the pairing gap parameter A,. Together with the Nilsson single-particle energies e~ and the pairing strength parameter G, A~ and A permit the calculation of the total energy of the system E qoPt(v):

EqoPt(v) = e ~ + 2

~_,

A2(v)

[ek-½G V2(v)]V2(v) - -

k>O,kC:v

(6)

G

and therefore also the different one-quasiparticle energies EqP(v): EqP(v) = EqtoPt(v)-min (E,~o°,(k)}.

(7)

The BCS equations were solved with a set of 40 single-particle states and the pairing

E. Kaerts et al. / t65Dy

213

strength G was chosen in such a way ( G = 139.6 keV) that the theoretical pairing energy: P, (165) = 2 E tqoPt(165) - E qoPt(164) - E tqoPt(166)

(8)

matches the experimental o d d - e v e n mass difference of 817.4 keV. In table 10 the Nilsson single-particle spectrum is c o m p a r e d with the results from the BCS calculations. The single-particle excitation energies were calculated relative to the energy of the 7+[633] state. The one-quasiparticle excitation energies were calculated from relation (7). 6.1.2. Theoretical 164Dy(d~p)165Dy cross sections. As described in ref. 36), the (d, p) stripping reaction transfers a single neutron to one of the empty states in the target nucleus. This reaction is thus especially useful to localise one-quasiparticle states with a pronounced particle character. Moreover, the distribution of (d, p) cross sections on the members of a rotational band is characteristic of the underlying one-quasiparticle configuration and a comparison of experimental intensity patterns with theoretical ones often allows the identification of the intrinsic structure of the rotational band. Therefore, the theoretical 164Dy(d, p)165Dy cross sections were calculated and c o m p a r e d with the experimental 164Dy(d, p) J65Dy data from Grotdal et al. 7). The (d, p) cross sections for rotational levels in 165Dy based on one-quasiparticle states v were calculated from the relation 36): (d0-/dl2(0))~ = 2(Cj,) ~ U ~ N 0 - , ( O ) ,

(9)

where cr~(0) is the cross section for the transfer of a neutron with orbital angular m o m e n t u m l to a spherical single-particle state with the remaining proton going in the direction 0. According to Grotdal et al. 7), the 0-j(90 °) values for the t64Dy(d, p)165Dy reaction (Q-value = 3.5 MeV) are: 0-0(90°) = 524 i~b/sr; 0-~(90°) = 300 txb/sr; 0-2(90 °) = 315 ixb/sr; 0-3(90°) = 300 ixb/sr; 0-4(90°) = 92 txb/sr; 0-s(90 °) = 23 txb/sr and 0-6(90°) = 23 I~b/sr. N is a normalisation constant; N = 1.5 [ref. 37)]. As shown in formula (5), deformed one-quasiparticle states are written as linear combinations of the spherical single-particle states. The theoretical coefficients Cj~ are listed in tables 8 and 9. The factor U 2. takes into account the quasiparticle character of the nuclear states in the neighbourhood of the Fermi level. It gives the probability that the deformed single-particle state (in 164Dy) is not occupied by a neutron pair: U2v = l[1 + (e, - A ) / ( e , - A)2 +/12) 1/2],

(10)

where e~ are the Nilsson energies. A and/1 were taken from ref. 38). The calculated values for U 2 are given in the fifth column of table 10. The factor 2 finally expresses the twofold degeneracy of the levels in the even-even target nucleus 164Dy. The theoretical 164Dy(d, p)165Dy cross sections for rotational levels in 165Dy ( I = j ) are given in table 10. They can be directly compared with the experimental

E~ (keV)

3022 2812 2599 1480 1247 600 178 0 846 1168 1376 1996 2440 2619 2904

K"[ Nn~A ]

~-[512] ½-[510] ½+[651] 3+[624] ~-[514] 5-[5121 ½-[521] ~+[633] ~-[523] ~+[642] ~-[521] ~+[651] ½+[660] ~-[532] ½-[530]

Nilsson formalism

TABLE 10

249.537 249.510 249.484 249.348 249.321 249.252 249.219 249.211 249.254 249.288 249.310 249.383 249.437 249.459 249.495

EtqPt (h~oo) 2483 2283 2080 1043 837 316 61 0 332 584 752 1313 1726 1895 2166

E qp (keV)

BCS formalism

0.99 0.99 0.98 0.97 0.96 0.92 0.82 0.74 0.19 0.10 0.08 0.03 0.00 0.00 0.00

U2

0

0

56

199

0 0 0

5

104 384 50

j=3

2 91

j=½

7 20 ~0 0 0 0 0

1 91

370 183 255

40 390 96 ~0 17 0 21 0 0 0 0

54 84 23

do'/df2 (0 = 90 °) (la,b/sr) j:~ j:7

(d, p)

Theoretical 165Dy one-quasiparticle spectrum and 164Dy(d, p)165Dy cross sections

9 6 82 5 59 14 13 11 9 3 2 1 0 0 0

j:9 20 20 4 0 1 2 1 ~0 1 0 ~0 0 0 0 0

1 0

4

33

5 45

"~

~-

E. Kaerts et al. / ~6SDy

215

TABLE 11 Experimental (d, p) cross sections for rotational levels in 165Dy below 1.4 MeV d~/dg~(O = 90 °) (~b/sr) ") Ebh

K~

(keV) 0.0

7+

108.155 184.254 533.492 570.265 573.584 911.968 1140.863 1256.498 1337.091

~II½ II+ ½+ 2~+

K ~ [ Nn._A ]

I =½

1 =3

I =I

I =7

164

15

66 b) 66 b) 5 30 24

99 218 143 c) 10 67 d)

12 e)

143 c) 12 e)

I =9

I =~

14 7 6 67 c)

5 6

7 8 81

85 69 53

103 121

I =? 44

7

~+[633] ½-[521] ~ [512] 2-[523] ½-[510] 7-[521] I+[642] ? 7-[512] ½+[651]

") The experimental (d, p) cross sections are taken from Grotdal et al. 7). Lines marked with h), c), o) or e) have a doublet structure (see table 7).

1 6 4 D y ( d , p)165Dy v a l u e s (0 = 90 °) from ref. 7) which - on the basis o f the rotational b a n d structure in J65Dy (see table 7) - have been arranged as shown in table 11.

6.1.3. Vibrational excitations and the quasiparticle-phonon interaction in 16SDy. Because o f the c o u p l i n g o f one-quasiparticle states K[NnzA] in 165Dy with the vibrational m o d e s (h, v) o f the e v e n - e v e n core 164Dy, a large n u m b e r o f vibrational excitations {K[NnzA], v} are expected to occur in 165Dy. Below 1500 keV, especially t h e K ~ = 2 + g a m m a vibration at 762 keV and the K ~ = 2 - octupole vibration at 977 keV will contribute. Rotational b a n d s based on pure o d d - A vibrational excitations have the following characteristics 39): (i) The rotational p a r a m e t e r A has almost the same value as for the rotational b a n d built on the one-quasiparticle state with which the vibrational excitation is associated. (ii) The d e c o u p l i n g p a r a m e t e r a (if K = ½) is very small: lal < 0.1. (iii) The members o f the rotational b a n d c a n n o t be p o p u l a t e d strongly via the (d, p) reaction. (iv) Rotational states with a pure q u a d r u p o l e vibrational intrinsic structure d e c a y principally to the m e m b e r s o f the rotational b a n d which is built on the associated one-quasiparticle state a n d the E2 transitions - having a collective character - are strongly e n h a n c e d with regard to asymptotically allowed E2 transitions between one-quasiparticle states. As a c o n s e q u e n c e o f the q u a s i p a r t i c l e - p h o n o n interaction, the simple picture o f a rotational b a n d b a s e d on a pure vibrational configuration will be disturbed. The presence o f a one-quasiparticle c o m p o n e n t (at least if it has a p r o n o u n c e d particle

216

E. Kaerts et al. / ~65Dy

TABLE 12 Asymptotically allowed M1 transitions between Nilsson states in ~65Dy Initial state

Final state

K ~[ NnzA ]

K ~[NnzA ]

2+[651] 2+[642] ~-[521l ~-[512] 2-[521] ½-[510]

~+[642l ~+[633] ½-[521] ~-1512] 2-[512] ½-[521]

character) in the originally pure vibrational state manifests itself most clearly in the occurrence of non-vanishing (d, p) cross sections for the associated rotational levels and in the change of their decay patterns. In 165Dy, the quasiparticle-phonon mixing often gives rise to strong, " u n e x p e c t e d " M1 transitions. Table 12 lists the onequasiparticle states which are connected with a large M1 matrix element 39). Apart from the above mentioned effects, the quasiparticle-phonon coupling also influences the values of the rotational and the decoupling parameters. In general, mixing between a vibrational excitation {K[Nn~A], p} of multipole character (A, v) and a one-quasiparticle state K'[N'n'zA'] occurs if the multipole operator Yx~ has a non-vanishing matrix element between K'[N'n'zA'] and the basis state of the vibration K[NnzA]. In the case of g a m m a vibrations for instance, the mixing conditions are: N ' = N, N + 2 and K ' = K +2, - K +2. The last requirement can only be fulfilled if K ( K ' ) = ½and K ' ( K ) = 3. The strongest interaction occurs if: AN=Anz =0

and

d K =zaA = 2 .

(11)

In ~65Dy, these conditions are fulfilled for a relatively large number of configurations so that the quasiparticle-phonon interaction is expected to play an important role.

6.2. INTERPRETATION OF THE INTRINSIC STRUCTURE IN 165Dy

In this section we attempt to interpret the intrinsic structure in ~65Dy in terms of one-quasiparticle and vibrational excitations with special emphasis on the quasiparticle-phonon interaction. Since the specific orbits involved near the Fermi surface are not connected by large Coriolis matrix elements, Coriolis mixing will not be considered in the present interpretation. A detailed theoretical study of the influence of both quasiparticle-phonon and Coriolis coupling on the intrinsic structure in 165Dy is given in ref. 41). 6.2.1. The 7÷[633], J-[521], 5-[512] and 5-[523] configurations. The main configuration of the intrinsic structure of the four lowest lying bands in ~65Dy was

E. Kaerts et al. / 165Dy

217

already identified in ref. 3). The present investigation supports these assignments: 7+[633] for the ground-state band, ½-[521] for the band at 108.2 keV, 25-[512] for the band at 184.2 keV and 25-[523] for the band at 533.5 keV. 6.2.2. Mixing of the 5-{~-[521], 2 +} and the 52-[523] configurations. In the adiabatic limit, the Ko + 2 g a m m a vibration associated with the ½ [521] configuration is roughly expected between 700 and 800 keV. According to relations (11) however, this vibrational excitation strongly interacts with the 25-[523] one-quasiparticle state. As a result, the intrinsic structure of the K = = ~s- band at 533.5 keV, which is mainly 25 [523], necessarily possesses a ~5 {~l [521], 2 +} component and therefore, collective E2 transitions to the ½ [521] band at 108.2 keV occur. Evidence for the presence of these extra collective E2 transitions (and therefore for the presence of a vibrational component) shows up in the large deviations which exist between experimental and theoretical (Alaga rules) [ref. 42)] relative E2 transition intensities from the K ~ = band at 533.5 keV to the ½-[521] band at 108.2 keV. These E2 transition intensities are listed in table 13. The relative M1 transition intensities to the ~ [512] band at 184.2 keV, on the other hand, are not significantly influenced by the ~-{~-[521], 2 +} c o m p o n e n t and are in good agreement with the predictions from the Alaga rules. 6.2.3. The 3+ {~7+[633], 2 +} and the 3+[651] configurations. According to table 10, the first K '~=3+ one-quasiparticle state in 165Dy (3+[651]) is only expected around 1.3 MeV so that the K = = ~ + band at 538.6keV was interpreted as 3+ 7+ + {~ [633], 2 } [ref. 3)]. This interpretation is supported by the intense transitions to the 7+[633] ground-state band. The one-quasiparticle configuration 2÷[651] is located at 1108.2 keV. Being a hole excitation, the absence of (d, p) feeding is not contradictory with this assignment (see table 11). The intrinsic structure of the K = = 3+ ~ band at 538.6 keV is expected to be almost purely vibrational. This is in total agreement with the fact that the rotational parameter of this band (A = 9.18 keV) is very close to the A-value of the ground-state band (A =9.30 keV) and with the correspondence between the experimental and theoretical relative E2 transition intensities in table 13. A small quasiparticle-phonon mixing between the 3+{7+[633], 2 +} and the 3+[651] configurations on the other hand explains the E1 decay from the K = = 3+ band at 538.6 keV and the transitions from the K ==3+ band at l l 0 8 . 2 k e V to the ground-state band and to the band at 538.6 keV. 6.2.4. Mixing of the 3- {~-[521], 2 +} and the 3-[521] configurations. A first K ~ = 3- band is observed at 573.6 keV. It comprises the levels at 573.6 keV ( I = 3), 628.8 keV ( I =25) and 705.9 keV ( I =7). According to table 11, these levels have (d, p) cross sections that suggest a mainly 3-[521] one-quasiparticle structure. It must be noticed however that this one-quasiparticle identification is not straightforward since it cannot explain the relative large (d, p) cross section for the I = = 25- level at 628.8 keV. The K ~ = 3 - band at 573.6 keV principally decays to the ½-[521] band at 108.2 keV via M I ( + E 2 ) transitions 9). Such a decay gives indication for a mixed 3-[521]+ 3-{½-[521], 2 +} structure. The strong M1 transitions result from the large M1 matrix

E.

218

K a e r t s et

al. / 16SDy

TABLE 13

Comparison between some theoretical a) and experimental relative y-transition intensities in 165Dy Initial level

Final level

Rel. intensities Multipolarity

E x (keV)

1, K '~

E x (keV)

533.492

5 ~5~,

108.155 158.589 180.923 297.683 184.254 261.770

607.624

2,75-2

158.589 180.923 297.683 337.163 184.254 261.770

/, K = ~, 1 -

E2

1.00 (13)

1.64

E2

1.00 (12)

1.00

0.0 83.396

648.972

7 3+ ~,~

0.0 83.396 186.095

0.41 0.02

M1

1.00 (10)

1.00

0.22 (3) 0.21 (3)

0.19 0.72

E2

1.00 (13)

1.00

7 ~12, 9 ~13, 5 25 2,

E2

0.53 (9)

0.15 0.03

_5 9 ~5 3,

3, 3+

1.22 (20) 0.15 (3)

M1 E2

261.7702,27 360.630

583.996

E2 E2

7 5 3,~ 2,3_2!5 ~1~,

360.630 9, 3 -

I (th.)

3 ~1~, 5 2t ~, v~, ~t 5 252,

7 ~5 ~, 9 ~5 ~,

702.892

I (exp.)

~,7~7+ 9 27+ 2, ~, 7+ 92, _7+ 2 ~1, 7+

E2

0.26 (4)

M1

1.00 (10)

1.00

M1

0.93 (13)

1.01

M1 M1

0.41 (6) 1.00 (10)

0.36 1.00

M1 E2

0.42 (10) 1.00 (10)

0.38 1.00

E2

0.47 (6)

0.57

E2

0.55 (12)

0.56

E2 E2

1.00 (10) 0.17 (2)

1.00 0.27

a) Theoretical relative transition intensities are calculated on the basis of the Alaga rules

42).

element between the 3-[521] and the I-[521] one-quasiparticle configurations while the smaller E2 contributions originate from the 3-{½-[521], 2 +} admixture. A second K " = 3 - band is located at 1088.0 keV. It comprises the 1088.0 keV (I =3) and 1135.8 keV (I =3) rotational levels while the 1 = 7 member is expected at 1207.7 keV (A = 9.56 keV). None of these levels has been observed in the (d, p) work. In agreement with its gamma decay pattern one can therefore conclude that the K~=32- band at 1088.0keV has a predominantly 3-{½-[521], 2 +} vibrational character with only a small admixture of 3-[521]. 6.2.5. Mixing of the ~ {s [512], 2 +} and the ~-[510] configurations. The intrinsic structure of the K " = ½ - band at 570.3 keV has previously been established as ½ {3-[512],2 +} [ref. 3)] with a large I-[510] component [refs. 4.7)]. The present results are consistent with this interpretation. The presence of a large (25%) ½-[510] component is not surprising since the I-[510] and the 5-[512] configurations are connected through a large E2 matrix element (relations 11 are fulfilled) resulting in a strong quasiparticle-phonon interac-

E. Kaerts et al. / t65Dy

219

tion between the I-[510] and the ½-{5-[512], 2 +} excitations. The presence of such a I-[510] c o m p o n e n t in the intrinsic structure of the band at 570.3 keV explains the strong decay of this band to the K ~ = I - band at 108.2 keY (I-[521]). Indeed, table 12 shows that the M1 matrix element between both one-quasiparticle configurations is large. 6.2.6. The 5+[642] configuration. Nilsson states originating in the spherical i13/2 shell are characterised by C13/2,6 expansion coefficients which are close to unity. Except C9/2.4, all the other coefficients practically vanish. Consequently, only the i ~ = 9+ and ~+ members of the associated rotational bands will have observable ( d , p ) cross sections. Such ( d , p ) patterns have been observed for the K ~=~7+ ground-state band 7) and for a K ~ = 5+ band at 912.0 keV (see table 11). Therefore, the intrinsic structure of both bands is interpreted as follows: 7+[633] for the ground-state band and 5+[642] for the band at 912.0 keV. The decay scheme of the 5+[642] band is characterised by strong M1 transitions to the ground-state band. 6.2.7. The ~ {3 [521],2 +} configuration. The K 7r - ~1 band at 1080.0keY has a rather complex decay scheme. Except for the ground-state band, transitions to all bands below 800 keV have been observed. Therefore we expect that the K ~__~lband at 1080.0 keV has a rather complex intrinsic structure. The main component is interpreted as I-{3 [521], 2+}. This interpretation is based on the systematic decay of the rotational levels of this band to the 3-[521] band at 573.6 keV and on the rotational parameters in table 7: A ( K ~ = ½-, 1080.0 keY) = A ( K ~ = 3-, 573.6 keY) = 11.0 keV. According to its decay scheme, the intrinsic structure of the K ~ -- I - band at 1080.0 keV probably also contains a small c o m p o n e n t of both the ½-[521] onequasiparticle configuration and the ½ {5-[523], 2 +} vibrational excitation. 6.2.8. The 1+{3_~-[512],2 } configuration. The three levels at l l40.9keV, 1166.9 keV and 1218.4 keV show a very similar decay pattern characterised by strong transitions to the I-[521] band at 108.2keV and to the ~ {~5- [512],2 +} band at 570.3 keV. In sect. 5 they were interpreted as the first three members of a K = -_- 2! + rotational band. According to table 10, the lowest K = = ½+ one-quasiparticle states are 1+[660] and ½+[651]. It is known that the ½+[660] state has a pronounced hole character in 165Dy while the ½+[651] configuration probably has a relative large decoupling parameter (a ~ 1) [ref. 39)]. Because of the small experimental a-value of -0.085 and the (d, p) population of the I = ½ and 3 levels, the K ~ = ½+ band at 1140.9 keV cannot be associated with these one-quasiparticle states. We have interpreted the intrinsic structure of the band at 1140.9 keV partly as ½+{5-[512], 2-}. In 164Dy, a K = = 2 - octupole vibrational band occurs at 977 keV [ref. 2)]. As in 162Dy [ref. 43)] and ~66Dy [ref. 41)], this band decays principally to the K "~= 2 + g a m m a band. Intrinsic excitations in ~65Dy originating from the coupling of a one-quasiparticle state with the K '~= 2 - octupole vibrational m o d e in 164Dy are expected from 1 MeV on. Assuming a similar decay pattern for these configurations as for the K "~= 2 - m o d e in t64Dy, the strong decay of the K ~ = I + band at l l 4 0 . 9 k e V to the ½-{~-[512],2 +} band at 570.3keV indeed supports the

220

E. Kaerts et al. / ~eSDy

½+{~-[512], 2 } assignment for this band. The small value of the decoupling parameter is consistent with a relative purely vibrational intrinsic structure. The (d, p) population of the levels at l139keV and l 1 6 2 k e V [ref. 7)] _ which presumably correspond with the I = ½ and 3 rotational levels of the band at 1140.9 keV - could not be explained. 6.2.9. Mixing of the 3 - { 7 [514], 2 +} and the 3-[512] configurations. The levels at 1256.6 keV and 1309.3 keV have been arranged in a K = = 3 band. The intrinsic structure of this band is interpreted as 3-{7-[514], 2 +} + 3 [512]. Since relations (11) are fulfilled, the Nilsson configurations 7 [514] and 3-[512] are related by a large E2 matrix element. Consequently, the 3-[512] configuration, which is only expected around 2.5 MeV, mixes with the 3 {7 [514], 2 +} g a m m a vibration and thus partly shows up at lower excitation energies. According to table 10, the (d, p) intensity pattern of the 3-[512] band is characterised by a very strong population of the I = 5 rotational level and a much less, but still clearly observable population of the I = 3 and ~7 rotational members. The experimental (d, p) cross sections of the I = 3 and 5 levels at 1256.6 and 1309.3 keV are in relatively good agreement with this picture. The I = 7 m e m b e r is expected around 1383 keV (A = 10.56 keV) but its (d, p) population is almost totally obscured by the strong population of the I ~=~+ level at 1380.9 keV (see subsect. 6.2.10). Further evidence for the presence of a 3 [512] c o m p o n e n t is given by the strong transitions to the 2-[512] band at 184.3 keV (see table 12). Although it probably has the largest contribution, there is no experimental evidence for the presence of a 3 {7 [514], 2 +} component in the intrinsic structure of the band at 1256.6 keV. 6.2.10. Mixing of the ~+[651] and the i+ {-2 [523], 2 } configurations. The /3decay of the ~3 + [411]p ground state of t65Tb to levels in ~65Dy has been studied by G r e e n w o o d et al. ~0). According to these authors, the levels at 1337.1 keV and 1400.3 keV are fed with a l o g f t value of 5.5 respectively 5.4. This indicates an allowed character for these /3- transitions which were interpreted as ~ [523]n~ 7 [523]p. Consequently, the intrinsic structure of the levels at 1337.1 keV and 1400.3 keV contains a contribution from the {5-[523], ,~3+[411]p, 7 [523]p} threequasiparticle configuration. Because the K = = 2- coupling of the two proton orbitals represents 96% of the K '~ = 2- octupole vibration in 164Dy, the K '~ = ~+ coupling of the above-mentioned three-quasiparticle configuration was interpreted as I~ 5 {~ [523],2 }. On the basis of the l o g f t values and the experimental decoupling parameter, Greenwood et al. ~o) argued that the K = =~t+ band at 1337.1 keV must also contain a considerable one-quasiparticle component. They suggested ½+[400] or ½+[660]. However, the intense (d, p) peaks at 1340 keV, 1402 keV and 1384keV, which correspond with the I =½, 3 and ~5 rotational levels at 1337.1 keV, 1400.3 keV and 1380.9 keV, are in contradiction with these one-quasiparticle assignments because they a p p e a r in 165Dy as deep-lying hole excitations. These experimental (d, p) cross sections are in good agreement with the theoretical pattern for a ½+[651] band as

E. Kaerts et al. / 165Dy

221

given in table 10. Even the ! =~9 member, which is expected around 1495 keV, is observed in the (d, p) experiment. The ½+[651] assignment is further supported by the agreement between the experimental (a = 1.45) and the theoretical (a-~ 1) [ref. 39)] decoupling parameters. Finally, it is worth mentioning that the ½+[651] Nilsson state originates in the g9/2 shell which in the spherical limit appears above the N = 126 energy gap.

6.3. DISCUSSION

From the interpretation of the intrinsic structure of the low-lying levels ( E x < 1.4 MeV) in 165Dy in the foregoing section, it is clear that considerable band mixing effects occur in ~65Dy. The quasiparticle-phonon interaction strongly influences the intrinsic structure in 165Dy. As a result, most rotational bands with an excitation energy above 500 keV possess a mixed intrinsic structure with both a one-quasiparticle character and a vibrational character. It is important to realise that as many as 6 of the 14 rotational bands below 1.4 MeV have a predominantly vibrational structure. The occurrence of such a large n u m b e r of low-lying vibrational states originates from the low K ~ = 2 + g a m m a vibrational and K ~ = 2 octupole vibrational energies in t64Dy, the relatively large number of one-quasiparticle states that exist below 600 keV in 165Dyand the energy-decreasing effect of the quasiparticlephonon interaction on the lowest-lying vibrational states in ~65Dy. Four out of the five K o - 2 g a m m a vibrational states associated with the one-quasiparticle states below 600 keV have been located. Only the 5~- {55 [523],2 +} configuration has not been observed. Because of the completeness of the level scheme below 1.4 MeV for I '~ = ½- levels, this configuration must appear above 1.4 MeV. In fig. 7, the experimental band-head energies and intrinsic structure (only the main configurations are given) below 1.4 MeV are compared with the theoretical predictions of Soloviev et al. 40). Although in some cases large deviations occur between experimental and theoretical band-head energies, the agreement between the intrinsic structure as discussed in subsect. 6.2, and the theoretical results as shown in fig. 7 is mostly satisfactory. It should, however, be noted that the contribution of the } {½ [521], 2 +} vibrational c o m p o n e n t to the intrinsic structure of the K '~ =~5- band at 533.5 keV is underestimated. Furthermore, the K = =~1+ band at 1337.1 keV has a strongly mixed ½+[651] +2~+{55 [523], 2 } intrinsic structure instead of a relative pure ½+{2 [523], 2-} vibrational structure. According to Soloviev et 5 [523],2 + } and ~-{½-[521],2 +} and the oneal. 4o), the vibrational states ~I - - {5 quasiparticle configuration 7-[514] are predicted at 1020 keV, 1030 keV and 1100 keV respectively. They are not shown in fig. 7. Experimentally, no evidence has been found for these configurations. Finally, it is interesting to note that the intrinsic structure of the three N = 99 isotones J65Dy ( Z = 66), 167Er ( Z = 68) [refs. 44,45)] and 169yb ( Z = 70) [refs. 46,47)] show a large degree of similarity. Indeed, in each case the same 8 rotational bands

222

E. Kaerts et aL / ~65Dy 1.4 _

1/2+[651]

-

-

'

~

_

99%(5/2-[523],2

(7/2 [514],2 +)

)

1.2 ( 5 / 2 - [512],2 - ) 3 / 2 + [651 ]

-

-

~

~

( 1 / 2 [521],2 +) ( 3 / 2 - [521],2 ÷)

61% + 7% (7/2+[633],2 +)

89% + 9% 3/2-

[521 ]

1.0

5/2

+

[642]

81% + 11%(1/2-[521],2 +) 0.8 93% + 6% 3 / 2 + [651] 64% + 31% 1 / 2 - [ 5 1 0 ] ~E 3 / 2 [521] (5/2 - [512],2 + ) (7/2+[633],2 +) 5 / 2 - [523]

0.6

89% + 4% ( 5 / 2 - [ 5 2 3 ] , 0 ) , 96%

0.4

90% + 8% ( 1 / 2 - [510],2 +) 0.2

5 / 2 - [512] 98% -

0.0 --

1/2-[521]

7 / 2 + [633]

EXPERIMENT

165 ~ . 66 ~ Y

98% THEORY

Fig. 7. Comparison of the experimental band-head energies and intrinsic structure (only main configurations are shown) below 1.4 MeV in ~65Dy with theoretical predictions of Soloviev et al. 4o).

E. Kaerts et al. / t65Dy

223

to 165Dy a n d 167Er, the first r o t a t i o n a l 169ybwith a p r e d o m i n a n t l y v i b r a t i o n a l structure a p p e a r s o n l y a b o v e 700 keV.

are o b s e r v e d b e l o w 1 MeV. I n c o n t r a d i c t i o n b a n d in

This results from the less collective character o f the K '~= 2 + g a m m a v i b r a t i o n in ~68yb (Ex = 984 keV) as c o m p a r e d to 164Dy (Ex = 762 keV) a n d 166Er (Ex = 786 keV).

7. Summary I n this c o m m u n i c a t i o n , a n u c l e a r structure s t u d y of 165Dy has b e e n presented. O n the basis o f t h e r m a l a n d average r e s o n a n c e n e u t r o n c a p t u r e results, a detailed a n d reliable level s c h e m e has b e e n e s t a b l i s h e d u p to 1.5 MeV. It i n c o r p o r a t e s 50 levels a n d 317 s e c o n d a r y y - t r a n s i t i o n s . F o r most levels, rather limited I '~ values have b e e n o b t a i n e d . Below 1.4 MeV, the level scheme is expected to be complete for I =½ a n d 3 levels o f b o t h parities. I n this energy region, 45 levels have b e e n a r r a n g e d into 14 r o t a t i o n a l b a n d s . T h r o u g h the c o m b i n a t i o n of the p r e s e n t (n, y) results a n d p r e v i o u s l y p u b l i s h e d (d, p) data, the i n t r i n s i c structure of these r o t a t i o n a l b a n d s c o u l d be successfully interpreted. I n this way, as m a n y as 6 r o t a t i o n a l b a n d s with a p r e d o m i n a n t l y v i b r a t i o n a l structure (5 g a m m a v i b r a t i o n s a n d 1 o c t u p o l e v i b r a t i o n ) have b e e n located b e t w e e n 500 a n d 1300 keV. It also a p p e a r e d that - as a c o n s e q u e n c e o f the q u a s i p a r t i c l e - p h o n o n i n t e r a c t i o n - most r o t a t i o n a l b a n d s above 500 keV have a strongly m i x e d i n t r i n s i c structure with b o t h a o n e - q u a s i p a r t i c l e a n d a v i b r a t i o n a l character. This work was s u p p o r t e d in part b y the U S D e p a r t m e n t of E n e r g y u n d e r contract DE-AC02-76CH00016.

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